摘要:

Filtration and soluble nutrient excretion were examined over a range of zebra mussel (Dreissena polymorpha) shell lengths (range = 6 to 32 mm) in experimental laboratory systems and combined with in situ shell length frequency distribution and areal estimates of zebra mussel population density to make predictions of overall areal filtration and soluble nutrient excretion rates in Lake Pepin, upper Mississippi River, USA. Zebra mussels removed seston and excreted ammonia and soluble phosphorus in laboratory systems. When normalized with respect to ash-free dry mass (i.e., μg g−1AFD mass d−1), smaller zebra mussels filtered seston and excreted soluble nutrients at a higher rate than larger zebra mussels. Although overall zebra mussel density is currently very low in Lake Pepin (~150 ind. M−2), lakewide chlorophyll filtration rates of ~ 7 mg m−2d−1were equivalent to chlorophyll loading into Lake Pepin via external sources and represented a turnover of 11 days for chlorophyll standing crop in the lake. Lakewide estimates of excretion of soluble phosphorus of ~ 3 mg m−2d−1by zebra mussels in Lake Pepin were comparable to internal phosphorus loading from anoxic sediments in other eutrophic freshwater aquatic systems. Our results suggest that zebra mussels are currently having a modest impact on phytoplankton dynamics and P and N recycling in this system.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663764

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Five species of fishes collected in 1998 from two tributaries of the Housatonic River, Berkshire County, Massachusetts were analyzed for total PCB content. The PCB content was significantly higher in fish in the stations closest to the tributary confluence, although there were no differences between the tributaries. Migration of fish between the mainstream and the tributaries is the most likely explanation for the presence of PCB contamination upstream of the source.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663765

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A multi-purpose colonization chamber is described for examining microbial community activity within streambed hyporheic and parafluvial regions, particularly where cherty or cobbly sediments prohibited standard coring techniques. The chamber allows 1) sampling of water chemistry and biofilm-colonized sediments from three depth intervals and 2)in situtime-course experiments with minimal disturbance within shallow groundwater environments beneath and adjacent to streambeds.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663766

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Cyprinids in small streams tend to segregate spatially to reduce competitive interaction and avoid predation. Understanding environmental parameters by which these fishes segregate provides valuable information on structure of fish guilds. Previous multivariate analyses of field data suggest spatial segregation occurs vertically within the water column and in relation to aquatic plants. In an experimental flume we controlled water flow and these two parameters to further investigate microhabitat partitioning of three cyprinid species: blacktail (Cyprinella venusta), bluntface (C. camura), and striped shiners (Luxilus chrysocephalus). Fish distribution relative to the environmental parameters was quantified with videography and expressed as percent occurrence. We observed significant differences across fish treatments in microhabitat selection relative to water flow and water column, and differences in species overlaps. These data support the idea that vertical position in water column is a major factor delineating resource gradients and maintaining habitat guilds. Blacktail shiners, however, showed a higher affinity to the upper water column than previously reported, and no differences were noted among the three shiners in their distributions relative to aquatic plants.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663767

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We quantified the diets of juvenile and adult largemouth bass (Micropterus salmoides), smallmouth bass (M. dolomieu), and spotted bass (M. punctulatus) in Skiatook Lake, Oklahoma in 1997 and 1999 to assess inter-annual and size-related differences in food resource use. The diets of juvenile and adult largemouth bass consisted mainly of fish, but juveniles consumed a significant number of dipterans during both years. Smallmouth bass and spotted bass adult diets were similar to each other in both years; crayfish and fish were the predominant food items. Juvenile smallmouth bass and spotted bass were mainly insectivorous with fish and crayfish also making up a proportion of the diet. Mean diet overlap was greater in 1999 compared to 1997. These findings are consistent with the expanding population hypothesis that predicts increased niche overlap.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663768

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Bluegill (Lepomis macrochirus), green sunfish (Lepomis cyanellus), largemouth bass (Micropterus salmoides), and longear sunfish (Lepomis megalotis) were sampled from 14 streams in southeastern Kansas for age determination and growth analysis. Growth rates for all species were highly variable among streams and were consistently lower than rates reported for these species from Missouri and Oklahoma streams. The results of this study provide important information on growth of centrarchids in Kansas streams.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663769

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The influence of a hypolimnetic reservoir discharge on breakdown of aspen (Populus tremuloides) leaves was investigated during the late summer and autumn at sites above and below a high mountain reservoir. During the two-year study, leaf packs (5-g envelopes) were secured to stream substrate in riffle/run areas. Leaves protected from invertebrates with fine mesh did not demonstrate differences in leaf loss between sites suggesting that microbial processing was equivalent. There were. however, significant differences in leaf loss in coarse mesh envelopes between sites, with losses higher at the site above the reservoir. Aquatic invertebrate communities colonizing the leaf packs also differed from above and below the reservoir suggesting that invertebrates played a role in the differing leaf loss. We hypothesize that during late summer and fall, leaf breakdown is slower below the reservoir because of the altered invertebrate community.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663770

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

During summer 1999, 5,004 landlocked alewives (Alosa pseudoharengus) were captured from 12 Connecticut lakes using horizontal gill nets with mesh sizes of 9.5, 12.7, 15.9, 19.1, 25.4, and 31.8 mm (bar measure). The most effective mesh size was 12.7-mm, capturing 3,035 alewives. The modal length of alewives caught in each mesh size increased as the mesh size increased from 9.5 to 25.4 mm. No alewives less than 70 mm total length or greater than 245 mm were captured. Modal lengths of selectivity curves estimated indirectly using the Holt model were 85, 114, 143, 172, and 228 mm for the 9.5-, 12.7–15.9-, 19. 1-, and 25.4-mm mesh sizes, respectively. Adding a 22.3-mm mesh and removing the 31.8-mm mesh is suggested to sample landlocked alewives between 100 and 245 mm in Connecticut lakes.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663771

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Over a five year period we compared summer temperature and dissolved oxygen (DO) at 10 sites within dense beds ofMyriophyllum spicatumL. to an unvegetated reference site in a moderately eutrophic Wisconsin lake. Average surface temperatures in the Eurasian watermilfoil beds were significantly elevated in two of the five years, while bottom temperatures were significantly depressed each year. Dissolved oxygen concentrations in surface layers of the bed were elevated by at least 1 mg L−1during roughly 30–40% of site-date visits, while DOs in the bottom layers were depressed on the average more than 50% of monitoring visits. Both depressed DOs and low DOs (< 3.0 mg L−1) in bottom layers were positively correlated with average annual air temperatures but were not directly related to variations in milfoil biomass. Dissolved oxygen and temperature appeared to be most severely impacted at shallow, densely vegetated sites close to shore.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663772

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Budgets and dynamics of nitrogen and phosphorus in Lake Donghu were investigated from Oct. 1997 to Sept. 1999. The water residence time was estimated to be 89 days in 1997–1998 and 124 days in 1998–1999. The total external loadings were 53 g N m−2yr−1and 3.2 g P m−2yr−1in 1997–1998, and 42 g N m−2yr−1and 3.1 g P m−2yr−1in 1998–1999. On average. about 80% of nitrogen and phosphorus input was from sewage outlets, while the rest was from land runoff and precipitation. Ammonium ion was the most abundant form of inorganic nitrogen in the sewage. The nutrient output was mainly through water outflow and fish catch. The percentages of nutrients in fish were estimated to be 7.8%-11.2% for nitrogen and 47.6%-49.6% for phosphorus. Lake Donghu has a very high nutrient retention (63% for nitrogen and 79% for phosphorus) mainly due to its closure and long water residence time. Sedimentation is an important nutrient retention mechanism in this lake. Using mass balance method, we estimated that denitrification of Lake Donghu involves about 50% of the retained nitrogen. Lake Donghu is rich in inorganic nitrogen and phosphorus and showed great seasonal variation.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663773

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor