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1.
Phytoplankton nutrient limitation experiments were performed from 1994 to 1996 at three stations in the Cape Fear River Estuary, a riverine system originating in the North Carolina piedmont. Nutrient addition bioassays were conducted by spiking triplicate cubitainers with various nutrient combinations and determining algal response by analyzing chlorophyll a production and 14C uptake daily for 3 d. Ambient chlorophyll a, nutrient concentration, and associated physical data were collected throughout the estuary as well. At a turbid, nutrient-rich oligohaline station, significant responses to nutrient additions were rare, with light the likely principal factor limiting phytoplankton production. During summer at a mesohaline station, phytoplankton community displayed significant nitrogen (N) limitation, while both phosphorus (P) and N were occasionally limiting in spring with some N+P co-limitation. Light was apparently limiting during fall and winter when the water was turid and nutrient-rich, as well as during other months of heavy rainfall and runoff. A polyhaline station in the lower estuary had clearer water and displayed significant responses to nutrient additions during all enrichment experiments. At this site N limitation occurred in summer and fall, and P limitation (with strong N+P co-limitation) occurred in winter and spring. The data suggest there are two patterns controlling phytoplankton productivity in the Cape Fear system: 1) a longitudinal pattern of decreasing light limitation and increasing nutrient sensitivity along the salinity gradient, and 2) a seasonal alternation of N limitation, light limitation, and P limitation in the middle-to-lower estuary. Statistical analyses indicated upper watershed precipitation events led to increased flow, turbidity, light attenuation, and nutrient loading, and decreased chlorophyll a and nutrient limitation potential in the estuary. Periods of low rainfall and river flow led to reduced estuarine turbidity, higher chlorophyll a, lower ambient nutrients, and more pronounced nutrient limitation.  相似文献   

2.
Macroalgal bloom dynamics in a highly eutrophic southern California estuary   总被引：3，自引：0，他引：3  
A 16-mo long monitoring study was carried out in Upper Newport Bay estuary (UNB), Orange County, California, to quantify the macroalgal community of a southern California estuary. Quarterly sampling began December 1996 at 8 stations along the main channel and tidal creeks ranging from the head to the lower end of UNB. At each station, two strata (one at high and one at low elevation) were surveyed. Macroalgal species abundance (% cover and biomass) and algal tissue nitrogen (N) and phosphorus (P) were measured. The algal community changed from sparse macroalgal cover during winter 1996 to larger patches dominated byEnteromorpha intestinalis in spring 1997. The community was characterized by a thick cover of macroalgae comprised ofE. intestinalis andUlva expansa in summer 1997 andU. expansa andCeramium spp. in fall 1997. UNB returned to sparse macroalgal cover by spring 1998. In summer and fall 1997, biomass ofE. intestinalis andCeramium reached over 1,000 g wet wt m−2 each, andU. expansa biomass exceeded 700 g wet wt m−2. Tissue N was high inE. intestinalis andU. expansa collected from UNB (≈3% dry wt) and higher inCeramium (≈3.5% dry wt). Tissue P in all three algae ranged from 0.24–0.28% dry wt. Tissue N∶P (molar) ratios inE. intestinalis andU. expansa ranged from 16.4 to 30.0 and inCeramium from 21.8 to 40.1. A field experiment was conducted in whichE. intestinalis was used as a bioassay of N and P availability. Algal tissue was cultured under known conditions and samples were deployed throughout the estuary and left for 24 h. Tissue N of algae from these bags showed a nominal increase in N with proximity to the primary nutrient input to the system, San Diego Creek (p=0.0251; r2=0.200). Our data indicate that UNB is already a highly eutrophic estuary, but macroalgal blooms in UNB may increase if more N is added to the system.  相似文献   

3.
Quarterly field sampling was conducted to characterize variations in water column and sediment nutrients in a eutrophic southern California estuary with a history of frequent macroalgal blooms. Water column and sediment nutrient measures demonstrated that Upper Newport Bay (UNB) is a highly enriched estuary. High nitrate (NO3 −) loads from the river entered the estuary at all sampling times with a rainy season (winter) maximum estimated at 2,419 mol h−1. This resulted in water NO3 − concentration in the estuary near the river mouth at least one order of magnitude above all other sampling locations during every seasons; maximum mean water NO3 − concentration was 800 μM during springer 1997. Phosphorus (P)-loading was high year round (5.7–90.4 mol h−1) with no seasonal pattern. Sediment nitrogen (N)-content showed a seasonal pattern with a spring maximum declining through fall. sediment and water nutrients, as well as percent cover of three dominant macroalgae, varied between the main channel and tidal creeks. During all seasons, water column NO3 − concentrations were higher in the main channel than in tidal creeks while tidal creeks had higher levels of sediment total Kjeldhal nitrogen (TKN) and P. During each of the four sampling periods, percent cover ofEntermorpha intestinalis andCeramium spp. was higher in tidal creeks than in the main channel, while percent cover ofUlva expansa was always higher in the main channel. Decreases in sediment N in both creek and channel habitats were concurrent with increases in macroalgal cover, possibly reflecting use of stored sediment TKN by macroalgae. Our data suggest a shift in primary nutrient sources for macroalgae in UNB from riverine input during winter and spring to recycling from sediments duirng summer and fall.  相似文献   

4.
The exchange of dissolved nutrients between marshes and the inundating water column was measured using throughflow marsh flumes built, in two microtidal Louisiana estuaries: the Barataria Basin estuary and Fourleague Bay. The flumes were sampled between September 1986 and April 1988, coincident with an extended period of low sea level on the Louisiana coast. The Barataria Basin estuary is in the later, deteriorating stage of the deltaic cycle, characterized by low freshwater inputs and subsiding marshes. Both brackish and saline marshes supplied dissolved organic nitrogen (DON), inorganic nitrogen (ammonium + nitrate + nitrite = DIN), dissolved organic carbon (DOC), and total nitrogen (as total Kjeldahl nitrogen = TKN) to the water column. The export of DIN is probably related to the N accumulated in earlier stages of deltaic development and released as these marshes deteriorate. Coastal brackish marshes of Fourleague, Bay, part of an accreting marsh system in an early, developmental stage of the deltaic cycle, exported TKN to the open water estuary in all samplings. This marsh apparently acted as a short-term buffer of DIN by taking up NH4 + in spring, when baywide concentrations were high, and supplying DIN to the estuary in summer and fall, when concentrations, in the bay were lower. Differences in phosphorus (P), DOC, and DON fluxes between these two estuaries were also observed. The Fourleague Bay site exported soluble reactive phosphorus (SRP) and total phosphorus (TP) and imported DOC. This P export may be related to remobilization of sediment-bound riverine P by the reducing, soils of the marshes. Fluxes of SRP at the Barataria Basin sites were variable and low while DOC was imported. Most imports of dissolved nutrients were correlated with higher upstream [source] concentrations, and flux rates were fairly consistent throughout the tide. Dissolved nutrient exports, did not correlate with upstream concentrations, though, and in many cases the flux was dominated by early, flood tide nutrient release. This pulsed behavior may be caused by rapid diffusion from the sediments early in the tidal cycle, when the sediment-water concentration gradient is largest. Interestuary differences were also seen in particulate organic matter fluxes, as the Fourleague Bay marsh exported POC and PON during all samplings while Barataria Basin imported these nutrients. In general, the magnitude and direction of nutrient exchanges in Louisiana marshes, seem to reflect the deltaic successional stage of the estuary.  相似文献   

5.
Nutrient limitation of the rhizophytic macroalgaPenicillus capitatus found associated with subtropical seagrass meadows in Bermuda was determined from enrichment assays and subsequent tissue analyses. The photosynthetic response ofP. capitatus to additions of inorganic nitrogen (N) or phosphorus (P), measured as oxygen evolution in closed incubation chambers, increased significantly in both the 16 h and 6 d experiments only with nitrogen enrichment. The average photosynthetic response for all treatments was virtually identical in the two experiments, indicating that there was not a significant time lag in nutrient uptake and that the short term (16 h) assay accurately reflected the longer term (6 d) photosynthetic response to nutrient enrichment. Average tissue nitrogen levels for the nitrogen-treated algae were 29% higher than the phosphorus-treated algae and 18% greater than the controls, corroborating the results from the photosynthesis assay.P. capitatus may acquire nutrients directly from sediment sources via rhizoid holdfasts. Ratios of total dissolved nitrogen (TN) to total dissolved phosphorus (TP) in pore water at 10 and 20 cm depths (6.1 and 4.5, respectively) indicate a nitrogen-limited nutrient pool. These low pore water TN:TP ratios may be a function of a limited sorptive capacity of the calcium carbonate sediments for phosphate, anthropogenic nutrient inputs, or high rates of denitrification, all of which would induce N rather than P limitation in these carbonate-rich sediments.  相似文献   

6.
We conducted a quantitative assessment of estuarine ecosystem responses to reduced phosphorus and nitrogen loading from sewage treatment facilities and to variability in freshwater flow and nonpoint nutrient inputs to the Patuxent River estuary. We analyzed a 19-year dataset of water quality conditions, nutrient loading, and climatic forcing for three estuarine regions and also computed monthly rates of net production of dissolved O2 and physical transport of dissolved inorganic nitrogen (DIN) and phosphorus (DIP) using a salt- and water-balance model. Point-source loading of DIN and DIP to the estuary declined by 40–60% following upgrades to sewage treatment plants and correlated with parallel decreases in DIN and DIP concentrations throughout the Patuxent. Reduced point-source nutrient loading and concentration resulted in declines in phytoplankton chlorophyll-a (chl-a) and light-saturated carbon fixation, as well as in bottom-layer O2 consumption for upper regions of the estuary. Despite significant reductions in seaward N transport from the middle to lower estuary, chl-a, turbidity, and surface-layer net O2 production increased in the lower estuary, especially during summer. This degradation of water quality in the lower estuary appears to be linked to a trend of increasing net inputs of DIN into the estuary from Chesapeake Bay and to above-average river flow during the mid-1990s. In addition, increased abundance of Mnemiopsis leidyi significantly reduced copepod abundance during summer from 1990 to 2002, which favored increases in chl-a and allowed a shift in total N partitioning from DIN to particulate organic nitrogen. These analyses illustrate (1) the value of long-term monitoring data, (2) the need for regional scale nutrient management that includes integrated estuarine systems, and (3) the potential water quality impacts of altered coastal food webs.  相似文献   

7.
Rapidly growing human populations have caused heavy modifications to the watersheds of many Mediterranean climate estuaries, subjecting them to excessive nutrient enrichment and harmful macroalgal blooms. Despite these impacts, comprehensive studies in these systems are rare and comparisons between systems are lacking. We surveyed five southern California estuaries that ranged in size from 93 to 1,000 ha and incorporated differing land usages and watershed sizes. We sampled environmental variables (sediment redox potential, organic content, total nitrogen and total phosphorus, water column nitrate, ammonium, and salinity) and macroalgal cover and biomass quarterly at three locations within each estuary over 15 months to compare spatial and wet vs. dry season patterns. Maximum mean water column nitrate concentration across all estuaries ranged from 47 to 1,700 μM, showing that all estuaries were highly enriched with nitrogen, at least at some times. Mean macroalgal biomass ranged from 0 to 1,500 g wet wt m?2. However, neither nutrient concentrations nor algal biomass showed consistent seasonal patterns as maximum values occurred in different seasons in different estuaries. Three-dimensional principal components analysis followed by regression analyses confirmed that macroalgal abundance was not directly related to water or sediment N concentrations. Rather each of these southern California estuaries showed individual patterns in all measured variables, which were most likely induced by a suite of physical modifications unique to each system and its watershed.  相似文献   

8.
One of the most serious threats to freshwater and marine ecosystems is high rates of anthropogenic nutrient loading, particularly nitrogen (N) and phophorus (P). One of the major freshwater sources of nutrients to Long Island Sound (LIS) is the Housatonic River (HR). Current management plans that call for reducing N inputs without reducing P inputs may change the N: P ratio in the water column and the pattern of algal nutrient limitation and species composition in the tidal portion of the river. To assess the current pattern of algal nutrient limitation in the HR estuary, nutrient bioassays were conducted in spring, summer, and fall at 5 sites throughout the tidal portion and adjacent LIS. Diatoms were a dominant taxon at all sites throughout the sampling period. Other seasonally important taxa include cyanobacteria, cryptophytes, and euglenoids. Phytoplankton in LIS were always strongly N limited and were co-limited by P in spring. During low flow (summer), phytoplankton in the lower HR estuary were N limited. Phytoplankton in the middle reaches showed no evidence of N or P limitation and were likely limited by other factors. In spring, phytoplankton in the upper HR estuary were P limited. Periods of N or P limitation were better correlated with periods of lower concentrations of nitrate or phosphate than with differences in N: P ratio. These results suggest that decreases in N concentration could increase the prevalence of N limitation throughout the estuary that in turn may reduce phytoplankton biomass and alter species composition of the phytoplankton.  相似文献   

9.
借助中国首次环球科学考察航次,在中大西洋航段现场对表层海水进行了添加N、P、Si的营养盐富集实验,通过实验过程中水体营养盐浓度、叶绿素a（Chl-a）浓度以及温度等参数的分析,探讨了实验海区浮游植物生长的营养盐限制作用。结果表明,添加N、P、Si都可造成实验水体中Chl-a浓度明显增大,且N对浮游植物生长的限制作用最明显,其次为P,Si的作用最弱。实验过程中水体N／P值的变化同叶绿素a浓度及浮游植物生长速度（R）没有可对比性,N／P值与后两者之间的相关性都差,可以认为水体中N／P值并不能单独限制浮游植物生长。实验水体温度同Chl-a浓度和R值间也缺乏相关性,表明水体温度同样不能控制浮游植物生长。  相似文献   

10.
Long-term interdisciplinary studies of the Rhode River estuary and its watershed in the mid-Atlantic coastal plain of North America have measured fluxes of nitrogen and phosphorus fractions through the hydrologically-linked ecosystems of this landscape. These ecosystems are upland forest, cropland, and pasture; streamside riparian forests; floodplain swamps; tidal brackish marshes and mudflats; and an estuarine embayment. Croplands discharged far more nitrogen per hectare in runoff than did forests and pastures. However, riparian deciduous hardwood forest bordering the cropland removed over 80 percent of the nitrate and total phosphorus in overland flows and about 85 percent of the nitrate in shallow groundwater drainage from cropland. Nevertheless, nutrient discharges from riparian forests downslope from croplands still exceeded discharges from pastures and other forests. The atomic ratio of nitrogen to phosphorus discharged from the watersheds into the estuary was about 9 for total nutrients and 6 for inorganic nutrient fractions. Such a low N:P ratio would promote nitrogen rather than phosphorus limitation of phytoplankton growth in the estuary. Estuarine tidal marshes trapped particulate nutrients and released dissolved nutrients. Subtidal mudflats in the upper estuary trapped particulate P, released dissolved phosphate, and consumed nitrate. This resulted in a decrease in the ratio of dissolved inorganic N:P in the estuary. However, the upper estuary was a major sink for total phosphorus due to sediment accretion in the subtidal area. Bulk precipitation accounted for 31 percent of the total nongaseous nitrogen influx to the landscape, while farming accounted for 69 percent. Forty-six percent of the total non-gaseous nitrogen influx was removed as farm products, 53 percent either accumulated in the watershed or was lost in gaseous forms, and 1 percent entered the Rhode River. Of the total phosphorus influx to the landscape, 7 percent was from bulk precipitation and 93 percent was from farming. Forty-five percent of the total phosphorus influx was removed as farm products, 48 percent accumulated in the watershed, and 7 percent entered the Rhode River. These nitrogen and phosphorus discharges into the Rhode River, although a small fraction of total loadings to the watershed, were large enough to cause seriously overenriched conditions in the upper estuary.  相似文献   

11.
In an experimental mesocosm system, we evaluated changes in morphology and tissue nutrient content (carbon [C], nitrogen [N], phosphorus [P]) of eelgrass (Zostera marina L.) as influenced by increased temperature and nitrate. During the late summer-fall growing season (14 weeks, August through mid-November), control plants were compared to plants grown at elevated temperatures (3°C to 4°C above ambient, based on 20-yr weekly means) and elevated water column nitrate enrichment (8 μM NO3 −, pulsed daily). Both increased temperature and increased nitrate led to declines in shoot density (by 40% and 48% for nitrate and temperature treatments, respectively), as well as decreased leaf and root production. High temperature promoted increased total C content of leaf tissues, whereas high nitrate increased the percentage of N in belowground tissues and depressed the C∶N ratio in aboveground tissues. The data indicated that increases in nitrate or temperature can significantly reduce the size ofZ. marine shoots and can also alter the internal C and N content. This reduction was not associated with significant increases in light-attenuating algae as we controlled epiphytic growth, so we suggest that a direct physiological mechanism or other mechanism was involved.  相似文献   

12.
A hypothesis was tested to determine if a relationship exists between rates of submarine groundwater discharge and the distribution of seagrass beds in the coastal, nearshore northeastern Gulf of Mexico. As determined by nonparametric statistics, four of seven seagrass beds in the northeastern Gulf of Mexico had significantly greater submarine groundwater discharge compared with adjacent sandy areas, but the remainder exhibited the opposite relationship. We were thus unable to verify if a relationship exists between submarine groundwater discharge and the distribution of seagrass beds in the nearshore sites selected. A second objective of this study was to determine the amount of nitrogen and phosphorus delivered to nearshore areas by submarine groundwater discharge. We considered new nutrient inputs to be delivered to surface waters by the upward flux of fresh water. This upward flux of water encounters saline porewaters in the surficial sediments and these porewaters contain recycled nutrients; actual nutrient flux from the sediment to overlying waters includes both new and recycled nutrients. New inputs of nitrogen to overlying surface waters for one 10-km section of coastline, calculated by multiplying groundwater nutrient concentrations from freshwater wells by measured seepage rates, were on the order of 1,100±190 mol N d−1. New and recycled nitrogen fluxes, calculated by multiplying surficial porewater concentrations by measured seepage rates, yielded fluxes of 3,600 ±1,000 mol N d−1. Soluble reactive phosphate values were 150±40 mol P d−1 using freshwater well concentrations and 130±3.0 mol P d−1 using porewater concentrations. These values are comparable to the average nutrient delivery of a small, local river.  相似文献   

13.
The distribution of mangrove biomass and forest structure along Shark River estuary in the Florida Coastal Everglades (FCE) has been correlated with elevated total phosphorus concentration in soils thought to be associated with storm events. The passage of Hurricane Wilma across Shark River estuary in 2005 allowed us to quantify sediment deposition and nutrient inputs in FCE mangrove forests associated with this storm event and to evaluate whether these pulsing events are sufficient to regulate nutrient biogeochemistry in mangrove forests of south Florida. We sampled the spatial pattern of sediment deposits and their chemical properties in mangrove forests along FCE sites in December 2005 and October 2006. The thickness (0.5 to 4.5 cm) of hurricane sediment deposits decreased with distance inland at each site. Bulk density, organic matter content, total nitrogen (N) and phosphorus (P) concentrations, and inorganic and organic P pools of hurricane sediment deposits differed from surface (0–10 cm) mangrove soils at each site. Vertical accretion resulting from this hurricane event was eight to 17 times greater than the annual accretion rate (0.30 ± 0.03 cm year−1) averaged over the last 50 years. Total P inputs from storm-derived sediments were equivalent to twice the average surface soil nutrient P density (0.19 mg cm−3). In contrast, total N inputs contributed 0.8 times the average soil nutrient N density (2.8 mg cm−3). Allochthonous mineral inputs from Hurricane Wilma represent a significant source of sediment to soil vertical accretion rates and nutrient resources in mangroves of southwestern Everglades. The gradient in total P deposition to mangrove soils from west to east direction across the FCE associated with this storm event is particularly significant to forest development due to the P-limited condition of this carbonate ecosystem. This source of P may be an important adaptation of mangrove forests in the Caribbean region to projected impacts of sea-level rise.  相似文献   

14.
We compared the distribution and nutrient status of native haplotype F ofPhragmites australis along the freshwater to mesohaline tidal marsh gradient of the Rappahannock River, Virginia, for comparison with the nonnative, invasive haploty M. Using GIS analysis of aerial photography and GPS-based ground truthing, we identified 55 separate clones of native haplotype F comprising a total of 3.68 ha (range 0.002–0.734 ha), all found in tidal wetlands where surface water salinity was 0 psu. We identified 219 separate clones of the invasive haplotype M covering 68.3 ha along the same stretch of river (range 0.004–11.86 ha), found in wetlands where salinity ranged from 0 to 11 psu. From 15 separate clones for each haplotype, average carbon content in leaves of the native was significantly higher than the invasive (43.90±0.08% versus 42.82±0.15%, F1,28=20.938, p<0.01), and nitrogen content was significantly lower (2.22±0.03% versus 2.58±0.07%, F1,28=11.972, p<0.01). The average C:N:P ratio for leaf tissue was 1100∶48∶1 for haplotype F and 1084∶56∶1 for haplotype M. Relative to the native, the invasive haplotype forms larger stands distributed throughout a broader estuarine reach and incorporates more nitrogen in leaf tissue. From a management standpoint, nativePhragmites protection should focus on deterring nonnative haplotype invasion through the minimization of both adjacent upland disturbance and nutrient enrichment in tidal freshwater marshes.  相似文献   

15.
Enteromorpha intestinalis is a bloom-forming species of macroalgae associated with eutrophication. The objective of this study was to investigate how this alga performs osmoregulation and nutrient uptake in order to proliferate under environmental conditions that covary with eutrophication. We quantified the response ofE. intestinalis to salinity, light, and nutrients. We performed two short-term (48 h) laboratory experiments (salinity alone and salinity × nutrients × light) to examine the algal responses of tissue water, potassium (K+), and nutrient (NO 3 − and total N) content. Tissue water content decreased with increasing salinity, and although K+ concentration decreased from the initial concentration, it decreased less with increased salinity treatment demonstrating two mechanisms to withstand short-term salinity fluctuation. The salinity × nutrient × light experiment showed that, in the short term, light had an interaction with tissue K+. Total tissue N content was positively related to N treatment level, and light did not affect total nutrient concentration. The effect of light was present whether the nutrients were present in the tissue as inorganic or organic forms. With reduced light, we hypothe size that the assimilation of inorganic to organic N was energy limited. The ability of this alga to take up available nutrients rapidly for growth and short-term osmoregulation, even under low light and salinity levels, helps to explain the bloom potential ofE. intestinalis.  相似文献   

16.
Seasonal phosphorus limitation occurs on the Louisiana continental shelf as a result of high nitrogen loads in the spring and early summer. Prior studies have assessed such nutrient limitation by laborious and time-consuming nutrient analyses, enzyme assays, and nutrient addition bioassays. We undertook surface (0.5–1 m) mapping of fast repetition rate fluorescence (FRRF) parameters to assess nutrient limitation in real time on the Louisiana continental shelf and Mississippi River plume from 29 June to 08 July, 2002 in an effort to further understand phytoplankton productivity in this region, as well as to better inform effective nutrient management strategies. Surface nutrient concentrations (NO3−, NO2−, NH4+, PO43−), chlorophyll a biomass, alkaline phosphatase (AP) activity, and four FRRF parameters: the maximum quantum yield of photochemistry (F v /F m ), the functional absorption cross section for PSII, the time constant for Q A reoxidation, and the connectivity factor, were measured during continuous underway mapping. Results from traditional methods to assess phytoplankton nutrient stress indicated widespread phosphorus limitation from the Mississippi River plume to the Atchafalaya River, manifested as high inorganic N/P ratios and elevated AP activities associated with phytoplankton biomass. The FRRF data indicated complex patterns of phytoplankton physiology that were likely driven by the rapidly changing conditions in local surface waters and heterogeneous phytoplankton community structure. Correlations of nutrient data and enzyme assays with FRRF parameters were significant but low, potentially due to differences in the manner and time scale with which nutrient limitation affects the different techniques used, indicating that further work is needed to interpret FRRF parameters in large, heterogeneous environments such as estuaries and continental shelves.  相似文献   

17.
Subtropical estuaries have received comparatively little attention in the study of nutrient loading and subsequent nutrient processing relative to temperate estuaries. Australian estuaries are particularly susceptible to increased nutrient loading and eutrophication, as 75% of the population resides within 200 km of the coastline. We assessed the factors potentially limiting both biomass and production in one Australian estuary, Moreton Bay, through stoichiometric comparisons of nitrogen (N), phosphorus (P), silicon (Si), and carbon (C) concentrations, particulate compositions, and rates of uptake. Samples were collected over 3 seasons in 1997–1998 at stations located throughout the bay system, including one riverine endmember site. Concentrations of all dissolved nutrients, as well as particulate nutrients and chlorophyll, declined 10-fold to 100-fold from the impacted western embayments to the eastern, more oceanic-influenced regions of the bay during all seasons. For all seasons and all regions, both the dissolved nutrients and particulate biomass yielded N:P ratios <6 and N:Si ratios <1. Both relationships suggest strong limitation of biomass by N throughout the bay. Limitation of rates of nutrient uptake and productivity were more complex. Low C:N and C:P uptake ratios at the riverine site suggested light limitation at all seasons, low N:P ratios suggested some degree of N limitation and high N:Si uptake ratios in austral winter suggested Si limitation of uptake during that season only. No evidence of P limitation of biomass or productivity was evident.  相似文献   

18.
Within the KUSTOS program (Coastal Mass and Energy Fluxes-the Land-Sea Transition in the Southeastern North Sea) 28 to 36 German Bight stations were seasonally surveyed (summer 1994, spring 1995, winter 1995–1996) for light conditions, dissolved inorganic nutrient concentrations, chlorophylla (chla), and photosynthesis versus light intensity (P:E) parameters. Combining P:E curve characteristics with irradiance, attenuation, and chlorophyll data resulted in seasonal estimates of the spatial distribution of total primary production. These data were used for an annual estimate of the total primary production in the Bight. In winter 1996 the water throughout the German Bight was well mixed. Dissolved inorganic nutrient concentrations were relatively high (nitrogen [DIN], soluble reactive phosphorus [SRP], and silicate [Si]: 23, 1, and 10 μM, respectively). Chla levels generally were low (< 2 μg l−1) with higher concentrations (4–16 μg l−1) in North Frisian coastal waters. Phytoplankton was limited by light. Total primary production averaged 0.2 g C m−2 d−1. Two surveys in April and May 1995 captured the buildup of a strong seasonal thermo-cline accompained by the development of a typical spring diatom bloom. High nutrient levels in the mixed layer during the first survey (DIN, SRP, and Si: 46, 0.45, and 11 μM, respectively) decreased towards the second survey (DIN, SRP, and Si: 30.5, 0.12, and 1.5 μM, respectively) and average nutrient ratios shifted further towards highly imbalanced values (DIN:SRP: 136 in survey 1, 580 in survey 2; DIN:Si: 13.5 in survey 1, 96 in survey 2). Chla ranged from 2 to 16 μg l−1 for the first survey and rose to 12–50 μg l−1 in the second survey. Phytoplankton in nearshore areas continued to be light limited during the second survey, while data from the stratified regions in the open German Bight indicates SRP and Si limitation. Total primary production ranged from 4.0 to 6.3 g C m−2 d−1. During summer 1994 a strong thermal stratification was present in the German Bight proper and shallow coastal areas showed unusually warm (up to 22°C), mixed waters. Chla concentrations ranged from 2 to 18 μg l−1. P:E characteristics were relatively high despite the low nutrient regime (DIN, SRP, and Si: 2, 0.2, and 1.5 μM, respectively), resulting in overall high total primary production values with an average of 7.7 g C m−2 d−1. Based on the seasonal primary production estimates of the described surveys a budget calculation yielded a total annual production of 430 g C m−2 yr−1 for the German Bight.  相似文献   

19.
The New River Estuary consists of a series of broad shallow lagoons draining a catchment area of 1,436 km2, located in Onslow County, North Carolina. During the 1980s and 1990s it was considered one of the most eutrophic estuaries in the southeastern United States and sustained dense phytoplankton blooms, bottom water anoxia and hypoxia, toxic outbreaks of the dinoflagellatePfiesteria, and fish kills. High nutrient loading, especially of phosphorus (P), from municipal and military sewage treatment plants was the principal cause leading to the eutrophic conditions. Nutrient addition bioassay experiments showed that additions of nitrogen (N) but not P consistently yielded significant increases in phytoplankton production relative to controls. During 1998 the City of Jacksonville and the U.S. Marine Corps Base at Camp Lejeune completely upgraded their sewage treatment systems and achieved large improvements in nutrient removal, reducing point source inputs of N and P to the estuary by approximately 57% and 71%, respectively. The sewage treatment plant upgrades led to significant estuarine decreases in ammonium, orthophosphate, chlorophylla, and turbidity concentrations, and subsequent increases in bottom water dissolved oxygen (DO) and light penetration. The large reduction in phytoplankton biomass led to a large reduction in labile phytoplankton carbon, likely an important source of biochemical oxygen demand in this estuary. The upper estuary stations experienced increases in average bottom water DO of 0.9 to 1.4 mg l−1, representing an improvement in benthic habitat for shellfish and other organisms. The reductions in light attenuation and turbidity should also improve the habitat conditions for growth of submersed aquatic vegetation, an important habitat for fish and shellfish.  相似文献   

20.
The Davis Pond Diversion (DPD) was constructed to divert Mississippi River (MR) water into the Barataria Basin to reduce the salinity in support of wetland restoration on the Louisiana coast. To assess the phytoplankton nutrient limitation in adjacent water systems and potential impacts of DPD, 12 seasonal nutrient-phytoplankton bioassay experiments were conducted from October 2003 to July 2004 using the natural phytoplankton assemblages from freshwater and brackish-water lakes, Cataouatche and Salvador, LA (USA), which receive Mississippi River water from the DPD, and from a nearby freshwater lake, Lac des Allemands, that does not. Dissolved inorganic nitrogen (N), phosphorus (P), and silicate (Si) were added with different combinations at Redfield ratios in 10-l microcosms. Nitrogen was found to be the sole or primary limiting nutrient in all 12 experiments. N and P colimitations were found in seven of 12 experiments, but N was always the stronger limiting factor. P limitation was never observed to be the sole limiting nutrient. The results showed that a low concentration of P and a relatively high concentration of N do not necessarily indicate only P limitation in these lakes. Lake Cataouatche and Lake Salvador were dominated by centric diatoms, and Anabaena spp. were detected at high levels, particularly in summer. Lac des Allemands was generally dominated by N-fixing Anabaena spp. and other cyanobacteria, and their biomass responded significantly to N addition but not to P addition, indicating that nitrogen fixation in Lac des Allemands may be inhibited by other factors such as iron. Our bioassay results demonstrate that whether a water body is N- or P-limited is the consequence of the nutrient status and not the salinity regime. The results suggest that the addition of nutrient-rich waters via diversions of Mississippi River water into these lakes might increase the frequency of algal blooms, including noxious and toxic freshwater cyanobacteria.  相似文献   

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