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1.
Expanding human activities along the freshwater to marine continuum of coastal watersheds increasingly impact nutrient inputs, nutrient limitation of primary production, and efforts to reduce nutrient over-enrichment and eutrophication. Historically, phosphorus (P) has been the priority nutrient controlling upstream freshwater productivity, whereas nitrogen (N) limitation has characterized coastal waters. However, changing anthropogenic activities have caused imbalances in N and P loading, making it difficult to control eutrophication by reducing only one nutrient. Furthermore, upstream nutrient reduction controls can impact downstream nutrient limitation characteristics. Recently, it was suggested that only reducing P will effectively control eutrophication in both freshwater and coastal ecosystems. However, controls on production and nutrient cycling in estuarine and coastal systems are physically and chemically distinct from those in freshwater counterparts, and upstream nutrient management actions (exclusive P controls) have exacerbated N-limited downstream eutrophication. Controls on both nutrients are needed for long-term management of eutrophication along the continuum.  相似文献   

2.
Nutrient over-enrichment has resulted in major changes in the coastal ecosystems of developed nations in Europe, North America, Asia, and Oceania, mostly taking place over the narrow period of 1960 to 1980. Many estuaries and embayments are affected, but the effects of this eutrophication have been also felt over large areas of semi-enclosed seas including the Baltic, North, Adriatic, and Black Seas in Europe, the Gulf of Mexico, and the Seto Inland Sea in Japan. Primary production increased, water clarity decreased, food chains were altered, oxygen depletion of bottom waters developed or expanded, seagrass beds were lost, and harmful algal blooms occurred with increased frequency. This period of dramatic alteration of coastal ecosystems, mostly for the worse from a human perspective, coincided with the more than doubling of additions of fixed nitrogen to the biosphere from human activities, driven particularly by a more than 5-fold increase in use of manufactured fertilizers during that 20-year period. Nutrient over-enrichment often interacted synergistically with other human activities, such as overfishing, habitat destruction, and other forms of chemical pollution, in contributing to the widespread degradation of coastal ecosystems that was observed during the last half of the 20th century. Science was effective in documenting the consequences and root causes of nutrient over-enrichment and has provided the basis for extensive efforts to abate it, ranging from national statutes and regulations to multijurisdictional compacts under the Helsinki Commission for the Baltic Sea, the Oslo-Paris Commission for the North Sea, and the Chesapeake Bay Program, for example. These efforts have usually been based on a relatively arbitrary goal of reducing nutrient inputs by a certain percentage, without much understanding of how and when this would affect the coastal ecosystem. While some of these efforts have succeeded in achieving reductions of inputs of phosphorus and nitrogen, principally through treatment of point-source discharges, relatively little progress has been made in reducing diffuse sources of nitrogen. Second-generation management goals tend to be based on desired outcomes for the coastal ecosystem and determination of the load reductions needed to attain them, for example the Total Daily Maximum Load approach in the U.S. and the Water Franmework Directive in the European Union. Science and technology are now challenged not just to diagnose the degree of eutrophication and its causes, but to contribute to its prognosis and treatment by determining the relative susceptibility of coastal ecosystems to nutrient over-enrichment, defining desirable and achievable outcomes for rehabilitation efforts, reducing nutrient sources, enhancing nutrient sinks, strategically targeting these efforts within watersheds, and predicting and observing responses in an adaptive management framework.  相似文献   

3.
Although algal blooms, including those considered toxic or harmful, can be natural phenomena, the nature of the global problem of harmful algal blooms (HABs) has expanded both in extent and its public perception over the last several decades. Of concern, especially for resource managers, is the potential relationship between HABs and the accelerated eutrophication of coastal waters from human activities. We address current insights into the relationships between HABs and eutrophication, focusing on sources of nutrients, known effects of nutrient loading and reduction, new understanding of pathways of nutrient acquisition among HAB species, and relationships between nutrients and toxic algae. Through specific, regional, and global examples of these various relationships, we offer both an assessment of the state of understanding, and the uncertainties that require future research efforts. The sources of nutrients potentially stimulating algal blooms include sewage, atmospheric deposition, groundwater flow, as well as agricultural and aquaculture runoff and discharge. On a global basis, strong correlations have been demonstrated between total phosphorus inputs and phytoplankton production in freshwaters, and between total nitrogen input and phytoplankton production in estuarine and marine waters. There are also numerous examples in geographic regions ranging from the largest and second largest U.S. mainland estuaries (Chesapeake Bay and the Albemarle-Pamlico Estuarine System), to the Inland Sea of Japan, the Black Sea, and Chinese coastal waters, where increases in nutrient loading have been linked with the development of large biomass blooms, leading to anoxia and even toxic or harmful impacts on fisheries resources, ecosystems, and human health or recreation. Many of these regions have witnessed reductions in phytoplankton biomass (as chlorophylla) or HAB incidence when nutrient controls were put in place. Shifts in species composition have often been attributed to changes in nutrient supply ratios, primarily N∶P or N∶Si. Recently this concept has been extended to include organic forms of nutrients, and an elevation in the ratio of dissolved organic carbon to dissolved organic nitrogen (DOC∶DON) has been observed during several recent blooms. The physiological strategies by which different groups of species acquire their nutrients have become better understood, and alternate modes of nutrition such as heterotrophy and mixotrophy are now recognized as common among HAB species. Despite our increased understanding of the pathways by which nutrients are delivered to ecosystems and the pathways by which they are assimilated differentially by different groups of species, the relationships between nutrient delivery and the development of blooms and their potential toxicity or harmfulness remain poorly understood. Many factors such as algal species presence/abundance, degree of flushing or water exchange, weather conditions, and presence and abundance of grazers contribute to the success of a given species at a given point in time. Similar nutrient loads do not have the same impact in different environments or in the same environment at different points in time. Eutrophication is one of several mechanisms by which harmful algae appear to be increasing in extent and duration in many locations. Although important, it is not the only explanation for blooms or toxic outbreaks. Nutrient enrichment has been strongly linked to stimulation of some harmful species, but for others it has not been an apparent contributing factor. The overall effect of nutrient over-enrichment on harmful algal species is clearly species specific.  相似文献   

4.
The global increase of noxious bloom occurrences has increased the need for phytoplankton management schemes. Such schemes require the ability to predict phytoplankton succession. Equilibrium Resource Competition theory, which is popular for predicting succession in lake systems, may not be useful in more dynamic environments, such as estuaries and coastal waters. We developed a mathematical model better suited to nonsteady state conditions. Our model incorporated luxury consumption of nonlimiting nutrients and cell starvation processes into a cell-quota-based nutrient-phytoplankton scheme. Nutrient pools described included nitrogen and phosphorus. Phytoplankton groups characterized in the model were a phosphorus-specialist, a nitrogen-specialist, and an intermediate group. We emphasized competition for nutrients under conditions of continuous and pulsing nutrient supply, as well as different nutrient loading ratios. Our results suggest that delivering nutrients in a pulsing fashion produces dramatic differences in phytoplankton community composition over a given period, that is, reduction of accumulated biomass of slower growing algae. Coastal managers may be able to inhibit initiation of slow-growing noxious blooms in estuaries and coastal waters by pulsing nutrients inputs from point sources, such as sewage treatment plants.  相似文献   

5.
A reduction in dissolved oxygen concentration is one of the most important direct effects of nutrient over-enrichment of coastal waters on fishes. Because hypoxia can cause mortality, reduced growth rates, and altered distributions and behaviors of fishes, as well as changes in the relative importance of organisms and pathways of carbon flow within food webs, hypoxia and anoxia can lead to large reductions in the abundance, diversity, and harvest of fishes within affected waters. Nutrient enrichment, however, typically increases prey abundance in more highly oxygenated surface waters and beyond the boundaries of the hypoxic zone. Because of this mosaic of high and low oxygen areas within a system, not only the actual oxygen concentration of bottom waters, but the spatial arrangement, predictability, and persistence of highly oxygenated, high productivity habitats, and the ability of fishes to locate and use those favorable habitats, will determine the ultimate effect of low oxygen on fish populations. Negative effects of hypoxia on fish, habitat, and food webs potentially make both fish populations and entire systems more susceptible to additional anthropogenic and natural stressors.  相似文献   

6.
Nutrient over-enrichment and cultural eutrophication are significant problems in the Danish marine environment. Symptoms of eutrophication include periods of hypoxia and anoxia in bottom waters, death of benthic-dwelling organisms during anoxia, long-term reductions in the depth distribution of macrophyte communities, changes in the species composition of macrophyte communities, and increases in reports of harmful algal blooms. In 1987 the Action Plan on the Aquatic Environment was adopted to combat nutrient pollution of the aquatic environment with the overall goal of reducing nitrogen loads by 50% and point source phosphorus loads by 80%. The Danish Aquatic Nation-wide Monitoring Program was begun in 1988 in order to describe the status of point sources (industry, sewage treatment plants, stormwater outfalls, scattered dwellings, and fish farms), ground water, springs, agricultural watersheds, streams, lakes, atmospheric deposition, and the marine environment. Another important aspect of the program was to document the effects on the aquatic environment of the measures and investments taken for nutrient reduction as outlined in the Action Plan. The monitoring program should determine if reductions in nutrients are achieved by the measures taken and should help decision makers choose appropriate additional measures to fulfill the objectives. Coordination with international programs and commissions is an important component of the monitoring program to meet internationally agreed upon reductions in nutrient inputs. The future and direction of the Danish National Aquatic Monitoring and Assessment Program will be to a large extent shaped by both the Water Framework Directive and Habitat Directive adopted by the European Union.  相似文献   

7.
Submarine groundwater discharge (SGD) has become increasingly recognized as an important source of freshwater and nutrients to coastal waters worldwide. Although groundwater nutrients have been found to cause algal blooms in many temperate coastal waters, little is known about the biological response to these nutrients in the tropics. On the leeward coast of Hawaii Island, SGD is the dominant freshwater and nutrient source to coastal waters. Kiholo Bay, HI and Kaloko-Honokohau National Historical Park, HI are two nearshore regions with well-documented SGD with high nutrient concentrations; however, little is known about how biological processes within the surface waters respond to these inputs. This study examined how potential gross primary production (pGPP), respiration (RESP), and potential metabolism (pMET) within surface waters differed inside and outside of groundwater plumes at these two sites and between wet and dry seasons. pGPP and RESP were both significantly higher within groundwater plumes, suggesting that SGD stimulated these biological processes; however, RESP responded to a much greater extent than pGPP, resulting in heterotrophic surface waters. RESP also varied seasonally, with greater rates during the dry season compared to the wet one; pGPP did not vary seasonally. Autotrophic conditions were found within groundwater plumes at Kiholo Bay, while heterotrophic conditions were found within them at Kaloko-Honokohau and were greater during the dry season. Overall, our results show that coastal biological processes respond to SGD and that their responses vary over short spatial and temporal scales.  相似文献   

8.
Human activities on coastal watersheds provide the major sources of nutrients entering shallow coastal ecosystems. Nutrient loadings from watersheds are the most widespread factor that alters structure and function of receiving aquatic ecosystems. To investigate this coupling of land to marine systems, we are studying a series of subwatersheds of Waquoit Bay that differ in degree of urbanization and hence are exposed to widely different nutrient loading rates. The subwatersheds differ in the number of septic tanks and the relative acreage of forests. In the area of our study, groundwater is the major mechanism that transports nutrients to coastal waters. Although there is some attenuation of nutrient concentrations within the aquifer or at the sediment-water interface, in urbanized areas there are significant increases in the nutrient content of groundwater arriving at the shore’s edge. The groundwater seeps or flows through the sediment-water boundary, and sufficient groundwater-borne nutrients (nitrogen in particular) traverse the sediment-water boundary to cause significant changes in the aquatic ecosystem. These loading-dependent alterations include increased nutrients in water, greater primary production by phytoplankton, and increased macroaglal biomass and growth (mediated by a suite of physiological responses to abundance of nutrients). The increased macroalgal biomass dominates the bay ecosystem through second- or third-order effects such as alterations of nutrient status of water columns and increasing frequency of anoxic events. The increases in seaweeds have decreased the areas covered by eelgrass habitats. The change in habitat type, plus the increased frequency of anoxic events, change the composition of the benthic fauna. The data make evident the importance of bottom-up control in shallow coastal food webs. The coupling of land to sea by groundwater-borne nutrient transport is mediated by a complex series of steps; the cascade of processes make it unlikely to find a one-to-one relation between land use and conditions in the aquatic ecosystem. Study of the process and synthesis by appropriate models may provide a way to deal with the complexities of the coupling.  相似文献   

9.
Surveys were conducted in April and June 1995 to quantify the uptake of dissolved nutrients in a highly turbid estuary (the Humber, United Kingdom) and to determine the factors controlling nutrient uptake rates. A combination of isotope labelling methods were used in conjunction with on-deck incubation techniques to estimate the uptake of dissolved nutrients (PO4 3?, NH4 +, NO3 ?, and urea) in surface samples collected from coastal waters. Similarly, isotope labelling and laboratory incubgation techniques were employed to estimate dissolved nitrogen uptake (NH4 +, NO3 ?, and urea) in surface samples collected from the estuary mouth. Nutrient uptake rates were at the low end of ranges for coastal and estuarine environments reported in the literature. Concentrations of chlorophyll and the availability of photosynthetically active radiation were identified as potentially important factors controlling the uptake rates of nutrients. Uptake rates of dissolved nitrogen in the Humber mouth appeared to be related to the location of smapling sites. Depletion rates of dissolved nutrients in situ were estimated on the basis of integrated water column nutrient uptake rates and indicated assimilation of up to 16% of nutrients in the entire water column. Estimated depletion rates did not indicate preferential loss of any of the nutrient species investigated.  相似文献   

10.
Baseflow and storm runoff fluxes of water, suspended particulate matter (SPM), and nutrients (N and P) were assessed in conservation, urban, and agricultural streams discharging to coastal waters around the tropical island of Oahu, Hawai‘i. Despite unusually low storm frequency and intensity during the study, storms accounted for 8–77% (median 30%) of discharge, 57–99% (median 93%) of SPM fluxes, 11–79% (median 36%) of dissolved nutrient fluxes and 52–99% (median 85%) of particulate nutrient fluxes to coastal waters. Fluvial nutrient concentrations varied with hydrologic conditions and land use; land use also affected water and particulate fluxes at some sites. Reactive dissolved N:P ratios typically were ≥16 (the ‘Redfield ratio’ for marine phytoplankton), indicating that inputs could support new production by coastal phytoplankton, but uptake of dissolved nutrients is probably inefficient due to rapid dilution and export of fluvial dissolved inputs. Particulate N and P fluxes were similar to or larger than dissolved fluxes at all sites (median 49% of total nitrogen, range 22–82%; median 69% of total phosphorus, range 49–93%). Impacts of particulate nutrients on coastal ecosystems will depend on how efficiently SPM is retained in nearshore areas, and on the timing and degree of transformation to reactive dissolved forms. Nevertheless, the magnitude of particulate nutrient fluxes suggests that they represent a significant nutrient source for many coastal ecosystems over relatively long time scales (weeks–years), and that reductions in particulate nutrient loading actually may have negative impacts on some coastal ecosystems.  相似文献   

11.
Nutrient stoichiometry and eutrophication in Indian mangroves   总被引：2，自引：2，他引：0  
Stoichiometry of dissolved nutrients in five important mangrove ecosystems of India (Sundarban, Bhitarkanika, Coringa, Pichavaram and Mangalavanam) was analyzed to describe the ecological and nutrient status of the inter-tidal mangroves in response to increasing human perturbations. The stoichiometric proportions of dissolved nutrients in mangroves highly deviated from the standard Redfield ratio (Si:N:P = 16:16:1), primarily because of the allochthonous nutrients derived from anthropogenic activities. In all mangroves, Si:N ratios were >1, which indicates that high silica is supplied from the terrestrial weathering to mangrove waters. Despite high phosphate loadings along with nitrogen from both point and non-point sources to mangrove waters, N:P ratios (Sundarban 11.43; Bhitarkanika 6.48; Coringa, 5.46; Pichavaram, 7.31 and Mangalavanam 4.64) demonstrate that phosphorus was a limiting nutrient in all mangrove ecosystems. The long-term nutrient analysis in Pichavaram mangrove water explains that the significant increase in dissolved nutrients since the 1980s is mainly derived from non-point sources (e.g., agriculture, aquaculture, etc.) that alter biogeochemical processes in this ecosystem. This study clearly reports that the ecological status of the Indian sub-continent mangroves is highly disturbed by anthropogenic impacts. Therefore, an appraisal of the nutrient ratios and sufficiency in mangroves facilitated an understanding of the current environmental conditions of coastal ecosystems, which further led to the proposal of the long-term observational research coupled with modeling to develop sustainable management strategies for conservation and restoration of mangroves.  相似文献   

12.
Nutrient fluxes and primary production were examined in Lake Illawarra (New South Wales, Australia), a shallow (Zmean=1.9 m) coastal lagoon with a surface area of 35 km2, by intensive measurement of dissolved nutrients and oxygen profiles over a 22-h period. Rates of primary production and nutrient uptake were calculated for the microphytobenthos, seagrass beds, macroalgae, and pelagic phytoplankton. Although gross nutrient release rates to the water column and sediment pore waters were potentially high, primary production by microphytobenthos rapidly sequesters the re-mineralized nutrients so that net releases, averaged over times longer than a day, were low. Production in the water column was closely coupled with the relatively low sediment net nutrient release rates and detrital decomposition in the water column. Dissolved inorganic nitrogen and silica concentrations in the water column are drawn down at the beginning of the day. The system did not appear to be light limited so photosynthesis occurs as fast as the nutrients become available to the phytoplankton and microphytobenthos. We conjecture that microphytobenthos are the dominant primary producers and, as has been shown previously, that the nutrient uptake occurs in phase with the various stages of the diatom growth.  相似文献   

13.
Climate impacts on coastal and estuarine systems take many forms and are dependent on the local conditions, including those set by humans. We use a biocomplexity framework to provide a perspective of the consequences of climate change for coastal wetland ecogeomorphology. We concentrate on three dimensions of climate change affects on ecogeomorphology: sea level rise, changes in storm frequency and intensity, and changes in freshwater, sediment, and nutrient inputs. While sea level rise, storms, sedimentation, and changing freshwater input can directly impact coastal and estuarine wetlands, biological processes can modify these physical impacts. Geomorphological changes to coastal and estuarine ecosystems can induce complex outcomes for the biota that are not themselves intuitively obvious because they are mediated by networks of biological interactions. Human impacts on wetlands occur at all scales. At the global scale, humans are altering climate at rapid rates compared to the historical and recent geological record. Climate change can disrupt ecological systems if it occurs at characteristic time scales shorter than ecological system response and causes alterations in ecological function that foster changes in structure or alter functional interactions. Many coastal wetlands can adjust to predicted climate change, but human impacts, in combination with climate change, will significantly affect coastal wetland ecosystems. Management for climate change must strike a balance between that which allows pulsing of materials and energy to the ecosystems and promotes ecosystem goods and services, while protecting human structures and activities. Science-based management depends on a multi-scale understanding of these biocomplex wetland systems. Causation is often associated with multiple factors, considerable variability, feedbacks, and interferences. The impacts of climate change can be detected through monitoring and assessment of historical or geological records. Attribution can be inferred through these in conjunction with experimentation and modeling. A significant challenge to allow wise management of coastal wetlands is to develop observing systems that act at appropriate scales to detect global climate change and its effects in the context of the various local and smaller scale effects.  相似文献   

14.
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15.
Nutrient enrichment of coastal waters is an example of the large-scale, highly complex environmental challenges facing decision makers today. Conventional monitoring networks and advanced observational capabilities permit the detection of changes in the environment at continental to global scales (e.g., hypoxia in the Gulf of Mexico, aerosol plumes stretching across the ocean, global atmospheric enrichment of carbon dioxide). Much more knowledge is needed, however, to fully understand the societal consequences of environmental change and of actions taken to address them. This paper discusses the emerging role of assessment in developing effective U.S. policy responses to large-scale, complex environmental change while improving the scientific understanding of the problem. In the cases of global climate change and coastal hypoxia, the U.S. Congress passed legislation authorizing assessments recognizing that decision making must proceed in the face of scientific uncertainty. Evaluating the state of knowledge is usually the first step in an assessment in order to provide a picture of what is known and where there are knowledge gaps. Assessments should also provide the policy maker with an idea of the level of uncertainty, how long it may take to reduce the uncertainty, what information is most critical to resolve, and the consequences and benefits of the various management options. In this paper I draw upon several examples from national assessments, including those of climate change impacts on the U.S. and relationships between Mississippi River water and Gulf of Mexico water quality, to illustrate the strengths and difficulties of using science and assessment to inform the policy process.  相似文献   

16.
To elucidate relationships between land cover and water quality along the central California coast, we collected monthly samples from 14 coastal waterway outlets representing various degrees of human development. Sites were distributed between three salinity categories, freshwater, estuarine, and marine, to better understand land cover-water quality relationships across a range of coastal aquatic ecosystems. Samples were analyzed for fecal indicator bacteria (FIB), dissolved nutrients, stable nitrogen isotopes in particulate organic matter, and chlorophylla (chla). Sediment samples from 11 sites were analyzed for the concentration of the anthropogenic organic contaminant perfluorooctane sulfonate and its precursors (ΣPFOS). While the data indicated impairment by nutrient, microbial, and organic contaminants at both agricultural and urban sites, the percentage of agricultural land cover was the most robust indicator of impairment, showing significant correlations (p<0.05) to FIB, nutrient, chla, and ΣPFOS levels. FIB densities were strongly influenced by salinity and were highest at sites dominated by agriculture and urbanization. Nutrient levels and chla correlated to both agricultural and urban land use metrics as well. Positive correlations among FIB, nutrients, chla, and ΣPFOS suggest a synergy between microbial, nutrient, and organic pollution. The results emphasize the importance of land management in protecting coastal water bodies and human health, and identify nutrient, microbial, and organic pollution as prevalent problems in coastal California water bodies.  相似文献   

17.
Groundwater discharge is increasingly recognized as a significant source of nutrient input to coastal waters, relative to surface water inputs. There remains limited information, however, on the extent to which nutrients and organic matter from each of these two flowpaths influence the functional responses of coastal microbial communities. As such, this study determined dissolved organic carbon (DOC) and nutrient concentrations of surface water runoff and groundwater from both an urbanized and a relatively pristine forested drainage basin near Myrtle Beach, South Carolina, and quantified the changes in production rates and biomass of phytoplankton and bacterioplankton in response to these inputs during two microcosm incubation experiments (August and October, 2011). Rainwater in the urbanized basin that would otherwise enter the groundwater appeared to be largely rerouted into the surface flowpath by impervious surfaces, bypassing ecosystem buffers and filtration mechanisms. Surface runoff from the developed basin was most enriched in nutrients and DOC and yielded the highest production rates of the various source waters upon addition to coastal waters. The metabolic responses of phytoplankton and bacterioplankton were generally well predicted as a function of initial chemical composition of the various source waters, though more so with bacterial production. Primary and bacterial productivities often correlated at reciprocal time points (24-h measurement of one with the 72-h measurement of the other). These results suggest human modification of coastal watersheds enhances the magnitude of dissolved constituents delivered to coastal waters as well as alters their distributions between surface and groundwater flowpaths, with significant implications for microbial community structure and function in coastal receiving waters.  相似文献   

18.
2005-2020年中国气象事业发展战略   总被引：3，自引：0，他引：3  
依据《中国气象事业发展战略研究总论卷》[1]的概述,在深入分析了中国气象事业的现状、国家需求和世界科技发展趋势的基础上,提出了“坚持公共气象的发展方向,大力提升气象信息对国家安全的保障能力,大力提升气象资源为可持续发展的支撑能力”的战略思想,明确了战略目标和战略任务,凝炼了重点工程和战略措施。  相似文献   

19.
Hydrography of the eastern Arabian Sea and associated chemical and biological responses were studied during the withdrawal phase of summer monsoon 2003. The shelf region off the southwest coast of India (10°N–15°N) continued to exhibit upwelling of colder (<28.5 °C), nutrient rich (nitrate >2.0 μM, phosphate >0.8 μM, silicate >4.0 μM) and relatively low oxygenated waters (~180 μM). The vertical advection of nutrients, coupled with anthropogenic terrestrial inputs, enhanced the levels of chlorophyll and primary productivity near the coastal margin off Cochin. The influence of both natural and anthropogenic nutrient loadings on the coastal system of the western continental shelf of India leads to eutrophication and hypoxia with negative impacts on the environment in general and fisheries in particular.  相似文献   

20.
Water quality monitoring in Hanalei Bay, Kaua`i (Hawai`i, USA) has documented intermittent high concentrations of nutrients (nitrate, phosphate, silica, and ammonium) and fecal indicator bacteria (FIB, i.e., enterococci and Escherichia coli) in nearshore waters and spurred concern that contaminated groundwater might be discharging into the bay. The present study sought to identify and track sources of nutrients and FIB to four beaches in Hanalei Bay and one beach outside the bay, together representing a wide range of land uses. 223Ra and 224Ra activity, salinity, nutrient and FIB concentrations were measured in samples from the coastal aquifer, the nearshore ocean, springs, the Hanalei River, and smaller streams. In addition, FIB concentrations in beach sands were measured at each site, and the enterococcal surface protein (esp) gene assay was used to investigate whether the observed FIB originated from a human source. Nutrient concentrations in groundwater were significantly higher than in nearshore water, inversely correlated to salinity, and highly site specific, indicating local controls on groundwater quality. Fluxes of groundwater into Hanalei Bay were calculated using a mass-balance approach and represented at least 2–10% of river discharges. However, submarine groundwater discharge (SGD) may provide 2.7 times as much nitrate + nitrite to Hanalei Bay as does the Hanalei River. It may also provide significant fluxes of phosphate and ammonium, comprising 15% and 20% of Hanalei River inputs, respectively. SGD-derived silica inputs to the bay comprised less than 3% of Hanalei River inputs. FIB concentrations in groundwater were typically lower than those in nearshore water, suggesting that significant FIB inputs from SGD are unlikely. Positive esp gene assays suggested that some enterococci in environmental samples were of human fecal origin. Identifying how nutrients and FIB enter nearshore waters will help environmental managers address pressing water quality issues, including exceedances of the state Enterococcus water quality standard and nutrient loading to coral reefs.  相似文献   

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