摘要:

Third Sister Lake in southeastern Michigan has been a focus of ecological studies since 1904. In 1999, we surveyed several physical, chemical, and biological parameters of the lake and compiled data collected by University of Michigan students since 1975. Comparison of dissolved oxygen profiles from years 1927–29, 1939–42 to recent data (1992–99) indicate a decrease in maximum oxygenation of bottom waters at fall turnover (8 mg O2·L−1maximum 1927–29, 1939–42 vs. 4 mg O2·L−11980, 1992–93) and more rapid depletion of oxygen in the hypolimnion following stratification. In early studies, oxygen persisted (> 3 mg L−1) at all depths from mid-November to May (1927–29, 1939–42). There has been no evidence of spring mixing in recent years and bottom waters have become anoxic by late January. The diversity and density of offshore benthic organisms has declined from at least 12 species and an average density of 167000·m−2in 1927 to 4–5 species at 15144 · m−2in 1999. Overall, benthic populations shifted from the deepest portions of the lake (16–18 m benthos) to shallower depths and onlyChaoboruswas found at bottom contours > 10 m in 1999. Mean chloride concentration [Cl·] increased nearly 13-fold from 19 mg L−1to 241 mg L−1between 1981 and 1988, with 260 mg L−1recorded in 1999. Calculations of whole-lake stability incorporating increases in [Cl·] indicate that about 60% more energy would be required to mix the lake following ice-out in 1999 compared to 1981. During the winter-spring transition, net respiration dominated under ice (4.1 g C·m−2d−1) and immediately afterice-out(0.32 g C·m−2d−1)in 1999. The phytoplankton community was dominated by cyanobacteria (Oscillatoria) from February to April. Under ice cover, bacterial abundance increased with depth from an average of 4.17 × 105cells ml−1(1–5 m) to 18.9 × 105cells ml−1(15 m).

ISSN:1040-2381    

DOI:10.1080/07438140009354234

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Sixty lakes and ponds distributed throughout the Cape Cod peninsula were each sampled three times during 1996–1998 in order to determine the chemical conditions of the waterbodies. The study lakes, situated on either glacial moraine, glacial outwash plain or post-glacial sand accumulations, ranged in surface area from 3.6 ha to 301 ha and in maximum depth from 1 m to 26 m. The dominant ionic species in all lakes were Na+and Cl−, likely due to inputs from sea spray. Conductivity and the relative charge contribution from Na+, Cl−and Mg2+increased with distance out onto the peninsula, whereas the contribution due to Ca2+decreased along the same distance gradient. Concentrations of Mg2+were greater than those of Ca2+in the study lakes, and the concentrations of the latter cation were very low compared to other areas in the northeast U.S. Except for the eutrophic lakes situated on the post-glacial sand accumulations on the outer tip of Cape Cod, the water bodies were, in general, low in total phosphorus, total nitrogen and chlorophyll-a levels, had high Secchi disk depths, and were best classified as oligotrophic. The pH and alkalinity (except for lakes situated on the post-glacial sand accumulations) declined with distance out onto the peninsula. The mean pH and alkalinity of water bodies located closest to the mainland were 6.8 and 71 μeq·L−1, respectively, but declined to only 5.3 and-7.5 μeq·L−1on the outer Cape. Findings are compared to other studies in the northeast U.S.

ISSN:1040-2381    

DOI:10.1080/07438140009354235

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We applied wave theory to calculate the extent and frequency that we would expect wave-driven surface water movements to disturb the sediments in 36 Florida lakes covering a broad range of surface areas and mean depths. The calculated per cent of the lakebed subject to wave disturbance at one time or another ranged from 6 to 100% and the per cent of the time 50% of the lakebed was disturbed ranged from 0 to 65%. The large Florida lakes, Apopka, Okeechobee, and Istokpoga showed high levels of calculated wave disturbance, which was consistent with the conclusions of previous investigations. Historic water level fluctuations in Lake Apopka were calculated to have major effects on wave disturbance in that lake. The dynamic ratio (the square root of lake surface area in square kilometers divided by the mean depth in meters) was significantly related to various measures of wave disturbance in our sample lakes. For lakes with ratio values above about 0.8 the entire lakebed was subject to wave disturbance at least some of the time. The dynamic ratio was also related to lake water quality. We found that increases in the dynamic ratio were significantly related to decreases in water quality as measured by total phosphorus, total nitrogen, chlorophyll, and Secchi disk depth. Calculations of wind disturbance by waves need to be modified in lakes with extensive beds of macrophytes, where water levels change and in periods where climatic fluctuations result in changes in wind regimes.

ISSN:1040-2381    

DOI:10.1080/07438140009354236

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A paleolimnological analysis of Lac Ste. Anne and Lake Isle, two eutrophic lakes in central Alberta, Canada, confirmed that they were naturally eutrophic, but have become increasingly eutrophic after the 1960s as 27% and 24% of their watersheds, respectively, were developed for urban and agricultural purposes. This was shown by a predominance of Chironomidae head capsules indicating periodic anoxia in bottom waters, high abundances of eutrophic diatoms (e.g.,Aulacoseira granulata, Fragilaria crotonensis, Stephanodiscus niagaraeandS. parvus), and, in Lac Ste. Anne, an enrichment of pigments from filamentous cyanobacteria (e.g., myxoxanthophyll) in post-1960 sediments. Evidence of periodic anoxia in the profundal zone was also provided by a scarcity of reducible phosphorus in the sediments. Lac Ste. Anne showed the largest changes during the 1960s and 1970s, when increases were observed in the abundance of hyper-eutrophic diatoms (e.g.,S. parvus) as well as sedimentary phosphorus fractions and algal pigments. The changes in Lake Isle were similar, but more subtle. Results indicate that reduced anthropogenic activities would still result in eutrophic systems, but some improvements in water quality would be achieved, particularly in Lac Ste. Anne.

ISSN:1040-2381    

DOI:10.1080/07438140009354237

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Diatom and chrysophyte assemblages from sediment cores were analyzed to assess the long-term trends of lake water quality in French Pond (New Hampshire), Joes Pond (Vermont), and Kenoza Lake (Massachusetts) as part of the US EPA's EMAP-SW (Environmental Monitoring and Assessment Program-Surface Waters) program in the northeastern USA. Sediment characteristics and geochemical data were also examined to interpret past limnological and watershed changes. Geochemical data indicate that exports of ions from the watersheds have increased and the lakes have received higher trace metal inputs over the post-industrial period. Stratigraphic changes in common diatom and chrysophyte taxa indicate that, over the last century, distinct water quality changes have occurred. Using the diatom- and chrysophyte-based weighted averaging inference models developed for lakes in the northeast, past changes in assemblages were used to infer trends in lakewater total phosphorus (TP), pH, and CI. In French Pond, inferred TP, pH, and CI changes were small, whereas Joes Pond and Kenoza Lake have experienced major changes. The latter two lakes have become more eutrophic, and lakewater pH and CI have also increased from their background values. Inferred water quality changes are closely related to watershed disturbances and resulting eutrophication. Our study illustrates that the inference models developed in EMAP-SW can be successfully applied in establishing long-term water quality trends in lakes throughout the northeastern USA. These models and subsequent sediment core data will help lake managers to develop effective management plans and to establish suitable targets for the restoration of other lakes of concern.

ISSN:1040-2381    

DOI:10.1080/07438140009354238

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Limnological measurements were performed at five or six Missouri reservoirs in June-September 1992–1995 to examine the relation of light conditions and non-algal seston (NAS) to chlorophyll (CHL) and dissolved nutrient concentrations. NAS was estimated as the sum of non-volatile suspended solids and filterable (Whatman 934AH filter) suspended solids. Mean mixed layer irradiance (Imix) varied ≈20 fold among observations, largely due to variation in light attenuation by NAS. In 42% of the observations, Imixwas less than 7 E·m−2d−1, a range where light limitation is likely. NAS comprised 15–96% (mean= 58%) of total seston and accounted for 89% of the temporal and inter-site variation in Imix. NAS was strongly correlated to total phosphorus (TP) and soluble reactive phosphorus (SRP) concentrations (r= 0.91 and r=0.84, respectively, p<0.0001). When NAS > 5 mg·L−1or Imixwas < 5 E m−2d−1, SRP and dissolved inorganic N (DIN) were usually at concentrations capable of saturating algal nutrient uptake (SRP >3 μg·L−1, DIN >50 μg·L−1), suggesting light limitation replaced nutrient limitation under those conditions. Light limitation resulting from NAS in turbid lakes may alter the relationship of phytoplankton to phosphorus, yielding a CHL-TP relationship that is dome-shaped rather than asymptotic. Variation in the relation of NAS to TP will affect how CHL responds to nutrients in individual waterbodies.

ISSN:1040-2381    

DOI:10.1080/07438140009354239

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Hypolimnetic chlorophyll maxima are common in clear lakes and often occur at depths with between 1 and 0.1% of the surface incident light. Little is known, however, about the concentrations of chlorophyll in thermally unstratified mountain ponds and how these concentrations compare to epilimnetic and hypolimnetic concentrations in mountain lakes. The objectives of this study were to document the concentrations of chlorophyll in thermally unstratified ponds and stratified lakes in Mount Rainier National Park (MORA) and to compare the results with concentrations and distributions of chlorophyll in clear-deep lakes in the Oregon Cascade Range and the Sierra Nevada Range. Thirty-two ponds (<2.5 m deep) and 14 lakes(>9.9 m deep) were sampled primarily during the summers of 1992 to 1996 at MORA. Water samples from near the surface (0.1–0.5 m) of ponds and near the surface and near the bottom of lakes were collected over the deepest part of each system. One exception, Mowich Lake, was sampled at seven depths between the surface and 50 m (Z=58.6 m). Chlorophyll concentrations were low in all systems, but higher in ponds (average 1.8 μg·L−1) than in lakes. Chlorophyll concentrations were higher in hypolimnetic lake samples (average 0.7 μg·L−1) than in epilimnetic lake samples (average 0.2 μg·L−1). Elevated concentrations of chlorophyll in mountain ponds, relative to those in hypolimnetic lake samples, may have been influenced by increased nutrient availability from interactions at the mud-water interface and, in this park, defecation by elk that used many of the ponds as wallows. Mowich Lake showed a chlorophyll maximum (~1.5 μg·L−1) near the lake bottom. Based on Secchi disk clarity readings, the depth of 1.0% incident surface solar radiation was greater than the maximum depths of the ponds and lakes. Comparative data from other clear-deep lakes in the Oregon Cascade Range and Sierra Nevada Range suggested that deep-chlorophyll maxima (~1.5 μg·L−1) occurred at <1.0% and > 0.1% of the incident surface solar radiation, and that the typical maximum depths ranged between 75 and 140 m during thermal stratification.

ISSN:1040-2381    

DOI:10.1080/07438140009354240

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The effect of bird density on water quality parameters of Collins Lake was examined at three time scales: yearly, seasonally, and weekly. There was no relationship between bird sightings and either coliform bacteria or Secchi disc transparency on a seasonal or long-term (19 year) period. There was also no increase in spring chlorophyll levels over the 19 year period, even though the annual total bird sightings increased almost three times over that period. However, chlorophyll levels did increase during the ice-free season as shown by an almost doubling of fall chlorophyll levels between 1978 and 1997. Increased bird density is considered the most probable cause for these elevated fall chlorophyll levels. The increase in summer resident birds appeared to have a greater effect on chlorophyll levels than migratory birds. There was no observable effect of bird density on chlorophyll levels on a weekly basis, but the large number of other variables changing in the lake during the study period may obscure any trend on this time scale.

ISSN:1040-2381    

DOI:10.1080/07438140009354241

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor