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1.
Submerged macrophyte detritus is a major component of the organic matter entering shallow lakes. Plant litter decomposition is a complex process that is mediated by microorganisms and some invertebrates. However, the role that aquatic organisms play in the decomposition of macrophytes in shallow subtropical lakes is unclear. This study compared the decomposition rates of Potamogeton pectinatus and Chara zeylanica in a shallow lake (southern Brazil) and assessed the fungal biomass and the macroinvertebrate community associated with the detritus. Aliquots of both species were incubated in litter bags and placed in the lake. After 1, 7, 20, 40, 60, and 80 days of incubation, one set of litter bags was removed from the lake. In a laboratory, plant material was washed for the determination of decomposition rates, chemical characterisation, and quantification of microorganisms and invertebrates. After 80 days of incubation, there was no C. zeylanica detritus, with a decomposition that was four times faster than that of P. pectinatus. The chemical composition was also different between the two detritus, with P. pectinatus showing a higher concentration of nitrogen, phosphorus, organic matter, polyphenols, and carbon. The fungal biomass was similar between the two species. In total, 7502 invertebrates belonging to 27 taxa were sampled in this study. The composition and abundance of invertebrates was different between the two species. In conclusion, the chemical structure of the macrophyte species studied was important for the microorganisms’ and invertebrates’ colonisation. In addition, leaching had an important function in the initial degradation process.  相似文献   

2.
Nutrient enrichment and changes in riparian tree species composition affect many streams worldwide but their combined effects on decomposers and litter decomposition have been rarely assessed. In this study we assessed the effects of experimental nitrogen (N) enrichment of a small forest stream on the decomposition of three leaf litter species differing in initial chemical composition [alder (Alnus glutinosa), chestnut (Castanea sativa) and poplar (Populus nigra)], incubated individually and in 2-species mixtures during late spring-early summer. To better understand the effects of litter mixing on litter decomposition, component litter species were processed individually for remaining mass and fungal reproductive activity. Litter decomposition rates were high. Nitrogen enrichment significantly stimulated litter decomposition only for alder incubated individually. Differences among litter treatments were found only at the N enriched site where the nutrient rich alder litter decomposed faster than all other litter treatments; only at this site was there a significant relationship between litter decomposition and initial litter N concentration. Decomposition rates of all litter mixtures were lower than those expected from the decomposition rates of the component litter species incubated individually, at the N enriched and reference sites, suggesting antagonistic effects of litter mixing. Conidial production by aquatic hyphomycetes for each sampling date was not affected by nutrient enrichment, litter species or mixing. Aquatic hyphomycetes species richness for each sampling date was higher at the N enriched site than at the reference site and higher for alder litter than for chestnut and poplar, but no effect of mixing was found. Aquatic hyphomycetes communities were structured by litter identity and to a lesser extent by N enrichment, with no effect of mixing. This study suggests that nutrient enrichment and litter quality may not have such strong effects on decomposers and litter decomposition in warmer seasons contrary to what has been reported for autumn-winter. Changes in the composition of the riparian vegetation may have unpredictable effects on litter decomposition independently of streams trophic state.  相似文献   

3.
The decomposition of plant litter is a fundamental ecological process in small forest streams. Litter decomposition is mostly controlled by litter characteristics and environmental conditions, with shredders playing a critical role. The aim of this study was to evaluate the effect of leaf species (Maprounea guianensis and Inga laurina, which have contrasting physical and chemical characteristics) and water nutrient enrichment (three levels) on leaf litter chemical characteristics and fungal biomass, and subsequent litter preference and consumption by Phylloicus sp. (a typical shredder in tropical streams). Maprounea guianensis leaves had lower lignin and nitrogen (N) concentrations, higher polyphenols concentration and lower lignin:N ratio than I. laurina leaves. Phosphorus concentrations were higher for both leaf species incubated at the highest water nutrient level. Fungal biomass was higher on M. guianensis than on I. laurina leaves, but it did not differ among nutrient levels. Relative consumption rates were higher when shredders fed on M. guianensis than on I. laurina leaves, due to the lower lignin:N ratio and higher fungal biomass of M. guianensis. Consumption rates on M. guianensis leaves were higher for those exposed to low water nutrient levels than for those exposed to moderate water nutrient levels. Feeding preferences by shredders were not affected by leaf species or nutrient level. The low carbon quality on I. laurina leaves makes it a less attractive substrate for microbial decomposers and a less palatable resource for shredders. Changes in litter input characteristics may be more important than short-term nutrient enrichment of stream water on shredder performance and ecosystem functioning.  相似文献   

4.
Riparian invasion by non-native trees may lead to changes in the quality of leaf litter inputs into freshwater ecosystems. Different plant species may affect the community of decomposers and the rate of litter decay in different ways. We studied the microbial colonization and decomposition of leaf litter of the invasive to Lithuania Acer negundo and native Alnus glutinosa during 64-day litterbag experiments in the littoral zones of mesotrophic and eutrophic lakes. The decomposition of A. negundo leaf litter proceeded faster than that of A. glutinosa irrespective of differences in the trophic conditions of the lakes. The amount of terrestrial and cellulose-degrading fungi (during the initial period) and bacterial numbers (during the experiment) were higher on A. negundo leaves than on A. glutinosa in both lakes. Differences in the assemblages of aquatic fungi colonizing the leaves of both types might be one of the reasons causing variation in their decay. The trophic conditions of the lakes did not significantly determine the extent of differences in decomposition rates between the two leaf species, but affected the microbial decomposers. The sporulation rate and diversity of aquatic fungi, especially on A. glutinosa leaves, was higher in the mesotrophic lake than in the eutrophic lake, while heterotrophic bacteria were more numerous on the leaves in the eutrophic lake. Generally, differences in the colonization dynamics of heterotrophs and the faster decay of A. negundo litter than of A. glutinosa suggest that the replacement of native riparian species such as the dominating A. glutinosa by invasive A. negundo may cause changes of organic matter processing in the littoral zones of lakes.  相似文献   

5.
The tropical riparian zone has a high diversity of plant species that produce a wide variety of chemical compounds, which may be released into streams. However, in recent decades there has been an extensive replacement of tropical native vegetation by Eucalyptus monocultures. Our objective was to compare fungal colonization of Eucalyptus camaldulensis leaves with fungal colonization of native plant species from riparian zones in Brazilian Cerrado (savannah) streams. The fungal colonization and enzymatic activity significantly influenced leaf litter decomposition. Fungal sporulation rates from leaf litter varied significantly with leaf species, with E. camaldulensis showing the highest sporulation rate (1226 conidia mg−1AFDM day−1) and leaf mass loss (23.2 ± 0.9%). This species has the lowest lignin content and highest N concentration among the studied species. Among the studied native species, we observed the highest sporulation rate for Protium spruceanum (271 conidia mg−1AFDM day−1), Maprounea guianensis (268 conidia mg−1AFDM day−1) and Copaifera langsdorffii (196 conidia mg−1AFDM day−1). Overall, native plant species of the Brazilian Cerrado exhibited recalcitrant characteristics and a higher lignin:N ratio. Therefore, variations in the physical and chemical characteristics of the leaf litter could explain the higher decay rate and reproductive activity observed for E. camaldulensis. However, the detritus of this species were colonized almost exclusively by Anguillospora filiformis (99.6 ± 0.4%) and exhibited a reduction in aquatic hyphomycetes species diversity. Our results suggest that the disturbance in the composition of riparian vegetation and consequently, in the diversity of leaf litter input into streams, could change the patterns and rates of leaf litter utilization by microbial decomposers. These changes may have important consequences in the processing of organic matter and, consequently, in the functioning of freshwater ecosystems.  相似文献   

6.
Riparian zones are important interface areas between soil and stream systems. Few studies carried out in tropical and subtropical regions evaluate litter decomposition in both stream water and riparian soils. Herein, we assessed the effects of land cover on microbial activity on the decomposition of an exotic litter (Pinus elliottii pine needles only) in water and soils of a subtropical riparian zone. Leaf litter breakdown rates (k in d−1) were estimated for different land covers (Grassland without riparian vegetation, Grassland with riparian vegetation, Forest, and Silviculture). To assess the microbial influence on k, we used fine mesh litter bags with monospecific leaf litter of senescent pine needles. Streams in Silviculture land use showed high k values and orthophosphate, dissolved oxygen and water velocity accelerated the leaf litter breakdown in the stream system. The soil system of Silviculture, Forest, and Grassland with riparian vegetation land covers showed high k values due to the high moisture and litter stock on riparian soil. Only a minor difference between stream and soil systems highlights the significant changes and the negative effects of silviculture on subtropical riparian zones.  相似文献   

7.
The distribution and abundance of macrophytes, land-use beyond the riparian zone, characteristics of the riparian zone and selected channel properties have been studied in 9 streams flowing through an agricultural landscape in the north-eastern part of Slovenia. The streams studied supported a rich macrophyte community. Altogether, 53 plant taxa were observed on 93 km of the streams. Canonical correspondence analysis indicated that 10 out of the 11 parameters examined significantly influenced macrophyte distribution. Of these, substrate characteristics and riparian vegetation type were the most influential. Species composition analysis revealed that the majority of species indicated moderate nutrient load while, in the more strongly modified reaches, species indicating eutrophic conditions, i.e. Myriophyllum spicatum and different species of genus Potamogeton, were more abundant.  相似文献   

8.
土壤动物对鄱阳湖湿地冬季凋落物分解过程的影响   总被引：1，自引：0，他引：1  
为了研究湿地土壤动物对凋落物分解速率以及对土壤养分归还的影响,于2017年11月份在鄱阳湖湿地收集苔草(Carex cinerascens)、南荻(Triarrhena lutarioriparia)和芦苇(Phragmites australis) 3种植物的凋落物,利用凋落物袋法开展原位的模拟实验研究中使用了网孔大小分别为4.5 mm(大)和0.1 mm(小)的分解袋来对比分析土壤动物的影响结果表明:不同物种之间凋落物分解速率有差异,苔草的分解速率显著大于南荻和芦苇,南荻与芦苇的分解速率差异不明显;凋落物的分解速率与凋落物总有机碳和总氮的积累量(NAI_(TOC)/NAI_(TN))呈负相关,与残余凋落物质量呈负相关,与凋落物总磷含量呈正相关;凋落物总氮含量在不同物种凋落物中差异明显,表现为苔草芦苇南荻,并且与分解速率的大小关系相对应,因此高氮植物凋落物的分解速率较快;土壤动物能够提高分解速率,促进凋落物营养元素的释放,进而调节凋落物中C、N、P元素向土壤养分库的归还过程本研究将为湿地生态系统的营养元素循环研究提供科学数据.  相似文献   

9.
Alien plant invasions of riparian zones can trigger bottom-up effects on freshwater ecosystems through changes in leaf litter supply. Riparian zones of ponds are often invaded by alien species, and although these habitats are common, the effect of invasive alien species on ponds has rarely been studied. We performed a leaf litter experiment in a pond and compared within- and between-species variation in the breakdown rates of three native species (Alnus glutinosa, Phragmites australis and Typha angustifolia) and two aggressive alien invaders of riparian zones (Fallopia japonica and Solidago canadensis). The litter of S. canadensis decomposed faster than the litter of the other plants; more than 50 % of the S. canadensis biomass decomposed within a week. This contradicts the home-field advantage hypothesis, and we argue that the quality rather than the origin of litter might be the key factor driving breakdown rates. We also reported considerable intra-specific variation; old leaves (collected in spring after a partial aerial breakdown on stems) decomposed two to seven times slower than senescent leaves (collected in autumn just after abscission). The continuous seasonal supply of leaves of different quality into freshwaters may be disrupted by terrestrial invasions, especially if an invader forms monoculture stands and produces a highly palatable litter, as is the case with S. canadensis. This may fundamentally alter the resource dynamics in the pond environment through a rapid depletion of litter mass before the next litterfall.  相似文献   

10.
Temperate and tropical shallow lakes differ in several fundamental aspects with respect to management of eutrophication. High altitude tropical shallow lakes are a special case, showing similarities with temperate and tropical lakes. We studied the ecology of the eutrophic high-altitude tropical lake Yahuarcocha in the Ecuadorian Andes and evaluated the potential of biomanipulation to control eutrophication. With a toxin-producing Cylindrospermopsis bloom, low Secchi depth and low submerged macrophyte cover, Yahuarcocha is clearly in a turbid ecosystem state. Relatively low nutrient concentrations should theoretically allow for a shift to a clear water state through biomanipulation. Top-down control of phytoplankton by zooplankton, however, is complicated by the (1) absence of predatory fish, (2) fish community dominated by small poecelid species, (3) lack of a refuge for zooplankton from fish predation within the macrophytes, and (4) persistent, grazing resistant bloom of the cyanobacterium Cylindrospermopsis. In these aspects, lake Yahuarcocha is more similar to tropical shallow lakes, probably because water temperature is high relative to the mean air temperature and because of the absence of a cold season. The fish and macrophyte communities consisted almost entirely of exotic species. The exotic fish species probably stabilized the turbid state in the lake.  相似文献   

11.
The decomposition of plant litter is an important mechanism in regard to energy and nutrient dynamics of ecosystems. Silicon concentration of plant tissue can affect these processes by changing litter quality, i.e. nutrient stoichiometry and cellulose and phenols content. To determine which group of microbial decomposers benefits from high Si content in plants and how this impacts on animal decomposers, a batch experiment was conducted with reed leaf litter (Phragmites australis) differing in Si content in the presence/absence of invertebrate shredders (Gammarus pulex). Lipid concentration of G. pulex, in reed litter and fine particulate matter (FPOM) were examined. High Si concentration in reed resulted in a decline of gram positive bacteria in the heterotrophic biofilm and of gram negative bacteria in FPOM. The lipid composition in the next trophic level, the decomposer G. pulex, changed too, indicating a diet shift in favor of bacteria and algae with increasing litter Si concentration. Thus, basal decomposers were affected by the Si availability in plant resources, and these effects likely persist along the food chain, as FPOM is a dominant food supply for other groups, e.g. collectors. This impact of Si content on plant substrate quality for decomposer food webs may have global relevance, due to related modifications in carbon and nutrient cycling during litter decomposition.  相似文献   

12.
Biotic and abiotic factors are filters that prevent invasions in aquatic and terrestrial ecosystems. In this investigation we tested the hypothesis that the success of a non-native Poaceae (Urochloa subquadripara) is positively correlated with the richness of native macrophytes and negatively correlated with wind disturbance (fetch) and presence of riparian vegetation on coarse spatial scales. Our samplings were carried out in a tropical reservoir (Rosana Reservoir, Brazil). We first compared competing models using the Akaike criterion to find the main combinations of explanatory variables (native macrophyte richness, fetch, and presence of riparian vegetation) associated with the success of U. subquadripara. Then, we applied multiple regressions to assess the coefficient of determination of the best models selected according to the Akaike criterion. The probability of occurrence of U. subquadripara increased significantly with increases in the number of native macrophyte species, but decreased with fetch and the presence of riparian vegetation. Stand width and maximum depth of occurrence (indicators of the success of this Poaceae) were also positively related with native richness and negatively with fetch and riparian vegetation. Our results supported our expectation that wave disturbance is an important variable explaining U. subquadripara success. Because the less exposed sites are also more favorable for colonization by natives, positive relationships between the success of non-native species and native diversity emerge at the coarse scale. Taken together, our results support the theory of “biotic acceptance”; that is, favorable sites are more prone to colonization by both native and non-native species.  相似文献   

13.
Agricultural practices affect the integrity of riparian areas of small streams. In this study we tested the hypothesis that the increase of agricultural activities influences negatively the functional conditions of the low order streams in the Atlantic forest of southern Brazil. Litter bags with leaves of Nectandra megapotamica (Spreng.) Mez were located in eight streams with different amounts of woody vegetation and agriculture land uses in their riparian zones. After 7, 15 and 30 days, the litter bags were removed for identification of associated invertebrates and determination of decomposition rate. Decomposition rates were negatively influenced by agriculture in the riparian zone while primary production was positively influenced. On the other hand, the decomposition mediated by microorganisms did not vary along the degradation gradient. The abundance of collectors increased in streams adjacent to agricultural land while the abundance of shredders was decreased. Our results showed that algae biomass and leaf decomposition were sensitive to the replacement of native vegetation by agricultural use. However, the trophic structure of invertebrates was moderately sensitive to agricultural land use.  相似文献   

14.
There is major uncertainty in the responses of litter decomposition to the inundation regimes in field studies, mainly because of the difficulties in identification of the individual effect of duration and frequency using field studies alone. The interactive role of inundation regime and litter quality also remains unclear. The responses of mass loss to simulated inundation regime (duration and frequency) and litter quality were investigated in leaves of Carex brevicuspis and leaves and stems of Miscanthus sacchariflorus from Dongting Lake, China. Three litter types differing in litter quality were incubated under seven different inundations over 360 days (three single inundations of 90, 180, and 360 days; three repeated 180-day inundations of 2, 3, and 6 times; and no inundations) in a pond near Dongting Lake. Initial N and P contents were highest in C. brevicuspis leaves, intermediate in M. sacchariflorus leaves, and lowest in M. sacchariflorus stems, whereas the organic C, cellulose, and lignin contents were ranked in the opposite order among the three litter types. Decomposition rate was highest in M. sacchariflorus leaves (0.00222–0.00900 day−1), intermediate in C. brevicuspis leaves (0.00135–0.00500 day−1), and lowest in M. sacchariflorus stems (0.00080–0.00100 day−1). The decomposition rate of both C. brevicuspis and M. sacchariflorus leaves increased with increasing inundation duration or decreasing frequency. However, both duration and frequency of inundation had no effect on decomposition of M. sacchariflorus stems. At the end of the incubation, N mineralization was complete in leaf litters with increasing rates with increasing inundation duration or decreasing inundation frequency, but accumulation was found in M. sacchariflorus stems. Organic C decayed quickly in both leaf litters compared with the stem litter. These data indicate that inundation regime has no effect on the decomposition of refractory stem litter while prolonged and stable inundation stimulates the degradation of labile leaf litter.  相似文献   

15.
This study of litter decomposition was part of an extensive project examining the partitioning of rainfall, the associated chemistry, and litterfall in a dry sclerophyll eucalypt forest and a Pinus radiata plantation in southeastern Australia. The eucalypt species studied were Eucalyptus rossii, E. mannifera and E. dives. The components tested were Pinus radiata needles, leaves of the three eucalypt species, and the bark of E. rossii and E. mannifera. During the first 16 weeks of the decomposition experiment there was a rapid decrease in the concentrations of potassium, magnesium, sodium and phosphorus; this was attributed to leaching. During this period, concentrations of nitrogen and calcium increased for most components. After this period, decomposition became the dominant process, during which the concentrations of most elements increased. By the end of the experiment there was, compared with the initial values, a marked reduction in concentrations of sodium, magnesium and potassium for all eucalypt and pine litter. Calcium concentrations increased through time, with eucalypt bark showing a mid‐period decline. Phosphorus concentrations decreased for the eucalypt leaves but increased substantially for the pine needles and the eucalypt bark. For all components of both the eucalypts and pines, total nitrogen concentrations rose consistently throughout the decomposition period. This was attributed to the formation of nitrogen‐substituted lignin, which was more resistant to decomposition than the other nitrogen‐containing compounds, as well as some nitrogen being stored in the micro‐organisms responsible for decomposition. Because of loss of fragmented litter from the litter bags after 16 weeks, the weight changes could not be confidently measured after this period. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

16.
The vertical sediment profiles (10 cm) of the margins of three shallow subtropical lakes (Rio Grande, Brazil) with different trophic states and surrounding areas were evaluated to identify the effects of the allochthonous input on the methane concentration in the sediment. Sediment cores were collected to quantify the organic matter content (OM) and total carbon (TC), total nitrogen (TN), total phosphorous (TP) and methane (CH4) concentrations.The three lakes were distinguished according to the trophic status and classified as oligotrophic, dystrophic and eutrophic. The natural characteristics of the dystrophic and eutrophic lakes have been changed due to the allochthonous input of leaves and twigs (Eucalyptus sp.) and the excreta of birds, respectively. In the eutrophic lake, the allochthonous input contributed to high autochthonous production. The highest values of OM, TC, TN and TP were found in the superficial sediments of the dystrophic and eutrophic lakes. The accumulation of allochthonous organic matter in the littoral zone promoted changes in the vertical sediment profiles and contributed to increases in the CH4 concentrations in the sediment.  相似文献   

17.
We propose and validate a new sampling method to assess the presence, abundance and distribution of macrophytes in circular-shaped lakes according to the requirements of the Water Framework Directive (WFD2000/60/EC). The results of the macrophyte survey, and in particular of macrophyte diversity, obtained using this method are also discussed.The sampling is based on randomly selected transects homogeneously distributed around the perimeter of the lake. The number of transects is proportional to the lake's size. The method was validated on six Italian volcanic lakes using computational resampling procedures on a total of 126 transects.Using resampling procedures, we show that the proposed approach identifies more than 75% of the overall species richness through a moderate sampling effort. According to our results, Charophytes dominate aquatic vegetation in Italian volcanic lakes. Species diversity is highest at shallow depths, whereas the most abundant species, such as Chara polyacantha, are located at an intermediate depth between the shoreline and the maximum growing depth.  相似文献   

18.
Natural riparian forest wetlands are known to be effective in their ability to remove nitrate by denitrification and sediments with attached phosphorus via sedimentation. On the other hand, litter input and decomposition is a process of crucial importance in cycling of nitrogen and phosphorus in a forest ecosystem.In this study we investigated the amount of nitrogen and phosphorus entering the alder fen ecosystem through leaf litter and its decomposition and the removal capacity of nitrogen and phosphorus by measuring denitrification and sedimentation in the alder fen.We found an average input of leaf litter during fall 1998 of 226 g m−2 yr−1 DW with nutrient concentration of 0.17% P and 1.6% N. This means a yearly input of 0.4 g m−2 yr−1 P and 3.6 g m−2 yr−1 N. The decomposition of leaf litter using litter bags with small and large mesh size resulted in bags with macroinvertebrates (large mesh size) and without macroinvertebrates (small mesh size). After 57 days the litter bags with macroinvertebrates had a decomposition rate of 79%.Denitrification was measured in May and June of 1997 using the acetylene inhibition technique on intact soil cores and slurry-experiments. The average annual denitrification rate was 0.2 g m−2 yr−1 N using data from the core experiments. The denitrification rate was higher after addition of nitrate, indicating that denitrification in the riparian alder fen is mainly controlled by nitrate supply.The sedimentation rate in the investigated alder fen ranged from 0.47 kg m−2 yr−1 DW to 4.46 kg m−2 yr−1 DW in 1998 depending on the study site and method we used. Sedimentation rates were lower in newly designed plate traps than in cylinder traps. The alder fen also showed lower rates than the adjacent creek Briese. Average phosphorus removal rate was 0.33 g m−2 yr−1 P.Input sources for the surface water of the alder fen are sediment mineralization and decomposition of leaf litter; output sources are sedimentation and denitrification. This study showed that a nutrient input of 24.58 kg ha−1 yr−1 N, 8.8 kg ha−1 yr−1 P and 419 kg ha−1 yr−1 DOC into the surface water of the alder fen is possible. Alder fens cannot improve water quality of an adjacent river system. This is only true for a nearly pristine alder fen with the hydrology of 10 months flooded conditions and 2 months non-flooding conditions a year.  相似文献   

19.
Freshwater communities on remote oceanic islands can be depauperate due to the influence of biogeographic processes that operate over a range of spatial scales, influencing the colonization of organisms, and events that shape local freshwater assemblages. The consequences of this paucity in organism diversity for the functioning of these ecosystems are, however, not well understood.Here, we examine the relative decomposition rate of leaf litter of native vs. exotic origin by aquatic macroinvertebrates and microbial communities in an isolated and depauperate oceanic environment.Bags containing a standard amount of leaf litter of each of 10 tree species (5 native and 5 non-native species) were deployed on two streams. Two types of bags differing in mesh size were used to allow or prevent the access of leaf litter to macroinvertebrates, respectively. Over a period of 28 days, mass loss of leaf litter was similar in the two bag types suggesting that macroinvertebrates had little influence on the break down of leaf litter in this system. In addition, there was no difference in mass loss of leaf litter of native and exotic origin. Decomposition rates were highly species-specific suggesting that decomposition rates were related to inhibitory substance specific of each leaf species. Our results add to the wider literature by showing that in depauperate and isolated ecosystems, and in contrast to temperate continental ecosystems, decomposition of plant litter by aquatic macroinvertebrates is negligible.  相似文献   

20.
Excessive macrophyte biomass and cyanobacterial blooms associated with eutrophication and possibly exotic fish frequently compromise freshwater systems. In this study, 20 large (∼3.2 m3), replicated enclosures were used to investigate the effects of piscivorous Australian bass (Macquaria novemaculeata), planktivorous gambusia (Gambusia holbrooki (Girard)), benthivorous carp (Cyprinus carpio), and macrophyte removal on water quality, as well as trophic interactions within the enclosures. Fish effects on reservoir water quality were carp > gambusia > bass. Cryptomonads spp. (54,083 cells/mL) and Anabaena spp. (47,983 cells/mL) increased significantly (63 and 23 fold, respectively) in carp enclosures, possibly because of physiological adaptation to low light, high turbidity, total phosphorus concentrations (TP) and low TN: TP ratios (N-limitation); a consequence of carp benthic grazing. Carp and gambusia caused an unconventional shift from smaller to medium sized zooplankton (e.g. Boeckella sp., Bosmina meridionalis), possibly a result of copepod nauplius grazing. In the subtropical system studied, fish-induced nutrient recycling appears more important to the outcome of bio-manipulation than grazing impacts. Macrophyte harvesting unexpectedly decreased phytoplankton biomass linked to declines in Euglenophyta and diatoms (Asterionella spp.). Cyanophyta (Oscillatoriales spp./Anabaena spp.) increased in response to macrophyte harvesting and was consistent with findings on European lakes that Cyanophyta abundance tends to be higher in the absence of macrophytes. Results indicate exotic fish removal, nutrient loading control and macrophyte conservation is important in these aquatic systems to maintain high water quality.  相似文献   

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