Showing papers on "Secchi disk published in 1999"
TL;DR: In this article, the authors investigated the effect of fish removal on the Secchi disk transparency and the reduction of benthivorous fish on the lake bottom view in Dutch lakes.
Abstract: Eighteen shallow lakes in The Netherlands were subjected to biomanipulation, i.e. drastic reduction of the fish stock, for the purpose of lake restoration. The morphology and the nutrient level of the lakes differed, as did the measures applied. In some lakes biomanipulation was accompanied by reduction of the phosphorus loading. In all but two lakes, the Secchi disk transparency increased after the fish removal. Eight lakes (no phosphorus loading reduction, except for one lake) showed a strong and quick response to the measures: the bottom of the lake became visible (‘lake bottom view’) and there was a massive development of submerged macrophytes. In eight other lakes the water transparency increased, but lake bottom view was not obtained. In the biomanipulated lakes the decrease in total phosphorus and chlorophyll a and the increase in Secchi disk transparency were significantly stronger than the general trend occurring in Dutch lakes where no measures had been taken. The improvement in the Secchi depth and chlorophyll a was also stronger than in lakes where only the phosphorus load was reduced. The critical factor for obtaining clear water was the extent of the fish reduction in winter. Significant effects were observed only after >75% fish reduction. Success seems to require substantial fish manipulation. In such strongly biomanipulated lakes, wind resuspension of the sediment never prevented the water from becoming clear. No conclusion can be drawn with respect to the possible negative impact of cyanobacteria or Neomysis on grazing by Daphnia and consequently on water clarity. In all lakes where there had been a high density of cyanobacteria or years with a high density of Neomysis other factors such as insufficient fishery may explain why lake bottom view was not obtained. In all lakes with additional phosphorus loading reduction the fish stock has been reduced less drastically (15–60%). In these lakes the effects on transparency were less pronounced than in the lakes with > 75% fish removal. Daphnia grazing seems responsible for spring clearing in all clear lakes but one. In three lakes the reduction of benthivorous fish also increased the transparency. The factors that determine water clarity in summer are less obvious. In most clear lakes a low algal biomass coincided with a macrophyte coverage of more than 25% of the lake surface area. However, it was not clear what mechanism caused the low algal biomass in summer, although inorganic nitrogen concentrations were regularly found to be very low. Daphnia grazing in open water seemed to be of little importance for suppressing the algal biomass in summer. Although in most lakes the total phosphorus concentration decreased after the biomanipulation, the dissolved phosphorus concentration remained too high to cause phosphorus limitation of the algal growth. In four out of six clear lakes for which there are long-term data the transparency decreased again after 4 years. In one lake with lower nutrient levels the Secchi disk transparency increased over the years. However, the number of lakes with low nutrient levels is too small for conclusions to be drawn regarding the impact of nutrient levels on the stability of the clear water state.
259 citations
TL;DR: In this paper, a model was developed for predicting mean Secchi disk depth readings as a measure of water clarity for the summer months in Lake Mendota, Wisconsin, where the 20-yr (1976-1995) data set also included external phosphorus (P) loadings and in-lake April P concentrations as indices of lake nutrient status, and monthly (28 d) water column stabilities and Daphnia biomasses as indices for lake mixing and algal grazing potentials, respectively.
Abstract: Linear models were developed for predicting mean Secchi disk depth readings as a measure of water clarity for the summer months in Lake Mendota, Wisconsin. The 20-yr (1976‐1995) data set also included external phosphorus (P) loadings and in-lake April P concentrations as indices of lake nutrient status, and monthly (28 d) water column stabilities and Daphnia biomasses as indices of lake mixing and algal grazing potentials, respectively. June Secchi depths were mostly controlled by food web dynamics, which dictated whether the larger-bodied Daphnia pulicaria or the smaller-bodied D. galeata mendotaedominated during the spring clear-water phase. May Daphnia biomasses were significantly greater in D. pulicaria-dominated years than in D. galeata-dominated years; D. pulicaria-year biomasses were also greater during the summer months. The model for the midsummer (July‐August) months indicated that Secchi depths were inversely related to April P concentrations and positively related to midsummer Daphnia biomasses and lake stabilities. Scenarios for midsummer Secchi depths were tested using the observed minimum and maximum values for each predictor variate. While holding two variates constant, April P, Daphnia biomass, and lake stability each resulted in relatively similar Secchi ranges (0.81, 0.81, and 1.17 m, respectively). Our results suggest that summer water clarity in eutrophic Lake Mendota is controlled by interacting ecosystem processes linked to land use activities, lake food web dynamics, and climate.
72 citations
TL;DR: In this article, the authors compare results from a probability-and a non-probability-based Secchi transparency sampling of lakes in the northeastern geographic region of the United States and its three primary ecoregions.
Abstract: Reliable environmental resource estimates are essential to informed regional scale decisions regarding protection, restoration, and enhancement of natural resources. Reliable estimates depend on objective and representative sampling. Probability-based sampling meets these requirements and provides accuracy estimates. Non-probability-based sampling often is biased, thus less reliable, and potentially misleading. The authors compare results from a probability- and a non-probability-based Secchi transparency sampling of lakes in the northeastern geographic region of the United States and its three primary ecoregions. Results from these samplings are compared on the basis of sample representativeness relative to the regional lake population and subsequent reliability of lake condition estimates. Statistically derived sampling indicates the northeast lake population median lake size to be about 9.5 ({+-}2.3) ha and the Secchi disk transparency (SDT) to be about 2.4 ({+-}0.4) m. On the basis of judgment sampling estimates, the median SDT for lakes in the same area would be 4.2 m. However, only about 15% of the regional lake population based on statistically designed sampling estimates has a SDT {ge} 4.2 m. Estimate unreliability of this magnitude can have profound effects on lake management decisions. Thus, regional extrapolation of non-probability-based sampling results should be avoided.
54 citations
TL;DR: The results indicate that Bannister's linear equation can generally be used to partition and quantify the sources of turbidity in aquaculture ponds and suggest that the contribution of non-phytoplankton turbidity to SDV measurements in fertilized and fed aquac culture ponds can be more important than phytoplanka turbidity.
24 citations
TL;DR: In this paper, a three-year study was carried out during 1987-89 to obtain the basic ecological knowledge required for a sustainable lake management, where water and phytoplankton samples were collected from several depths of the water column at the deepest zone of the lake.
Abstract: In regions with high inter-annual climatic variability, lake management strategies should be based on scientific data covering the maximum range of lake dynamics. Lake Sanabria is a monomictic lake located in a gneiss-dominated glacial valley at 1000 m a. m. s. 1. in NW Spain. A three-year study was carried out during 1987–89 to obtain the basic ecological knowledge required for a sustainable lake management. Water and phytoplankton samples were collected from several depths of the water column at the deepest zone of the lake. Temperature and Secchi disk visibility, and total and dissolved inorganic nitrogen and phosphorus, chlorophyll a, and phytoplankton species composition and abundance (in laboratory) were determined monthly following standard limnological methods. Stratification began in March-April, with the thermocline stabilized at between 6–10 m, and lasted until November-December. The euphotic depth was higher than the mixing depth throughout the stratification period, except in the month previous to the water column mixing. The water residence time, estimated from the volume of the lake and the inflows and outflows, was between 0.48–0.67 years. However, during the months of highest rainfall (September-February) it was up to three times greater than during the same months of low rainy years. Nutrient concentrations in the water were very low throughout the year (52 μg 1−1 dissolved inorganic nitrogen, 6.1 μg 1−1 soluble reactive phosphorus, and 1.45 mg 1−1 soluble reactive silica) and dominated by the dissolved organic fractions, which was related to the inputs of organic materials from the densely forested catchment. The colour of the lake, 21–41 mg Pt 1−1, is also indicative of the relatively high amount of organic substances dissolved in the waters of the lake. A bloom of cyanobacteria (Microcystis flos-aquae, Aphanothece clathrata, Merismopedia tenuisssima, Synechococcus sp.) persisted in most of the water column during August 1988-March 1989, associated with the high residence time of the water. In contrast, the cyanobacteria bloom was limited to the mesolimnion for 3–5 months during 1987 and 1989. A model is proposed for the seasonal variation of the phytoplankton, which differentiates the seasonal trend during years of high water turnover from that of years with long residence time. Lake Sanabria is oligotrophic, based on a range of criteria (Secchi disk visibility, chlorophyll a concentration, total phosphorus concentration). However, during years of long water residence time (e.g. 1988), the annual input of total phosphorus is critical to maintain the characteristics of the lake. Short-term strategies for the management of lakes should take into account the inter-annual variability rather than averages as indicators to prevent the impact of increased nutrient inputs derived from changes in land and water use in the catchment area. Long-term strategies should also consider the potential changes in the lake’s dynamics, derived from the changes in the rainfall pattern caused by climatic changes.
20 citations
TL;DR: In this paper, water temperature, salinity, total dissolved solids, pH, dissolved oxygen, secchi disk depth, turbidity and total suspended solids were measured in the Wilderness and Swartvlei lake systems between 1991 and 1997.
Abstract: Measurements of water temperature, salinity, total dissolved solids, pH, dissolved oxygen, secchi disk depth, turbidity and total suspended solids were undertaken monthly in the Wilderness and Swartvlei lake systems between 1991 and 1997. The range of most water quality variables is wider than recorded in earlier studies. Potential causes are discussed for each variable, and include both anthropogenic modification of the quantity and timing of water movements within the lakes, as well as higher sampling and longer duration studies resulting in more accurate recording of natural variability. Historical data on total dissolved solids (1978 to 1990) were combined with data collected in these surveys to assess the occurrence of trends in relation to freshwater inflows. Long-term (19-year) changes in total dissolved solids have occurred in all lakes, with decreases during high runoff periods and increases during low runoff periods. There is little evidence of unidirectional change in total dissolved solids despite increased water abstraction from influent rivers.
20 citations
TL;DR: An analysis of Secchi disk transparency observations from 3 sites on the Lake Pontchartrain Causeway indicates that water clarity has increased at the north shore and mid-lake sites, but has not changed at the south shore sitc. as mentioned in this paper.
Abstract: An analysis of Secchi disk transparency observations from 3 sites on the Lake Pontchartrain Causeway indicates that water clarity has increased at the north shore and mid-lake sites, but has not changed at thesouth shore sitc. LouisinnaDepartment oFEnvirenmental Qualitydata from I986 through 1995 were uscd in the analysis. Further analysis indicates that the increased transparency was not caused by changes in salinity or wind speed. The best explanation for the observed increase is the cessation of shell dredging ln 1990. Lake Pontchartrain is an estuarine embayment located in southeastern Louisiana, north of metropolitan New OrleanS.The lake has a mean salinity of about 4%, mean depth of 3.7 m and surface areaof 1,630 km2 (Sikora and Kjerfve 1985). Several factors have contributed ta the environmental degradation of Lake Pontchartrain including urban and agricultural runoff. she1 1 dredging, saltwater intrusion, operation of the Bannet Carre Spillway and industrial discharges (Houck et a!. 1983). A major environmental concern has been an assumed long-term increase in turbidity based on Secchi disk transparency
16 citations
TL;DR: The reservoir was eutrophic according to all the criteria assessed and practices aimed at reducing phosphorus and sediment loadings are suggested to improve water quality.
Abstract: The trophic state of Clinton Lake was assessed. Typical longitudinal gradients were observed with nutrient concentrations (TN, TP, NO3-N, NH4-N, PO4-P) decreasing from the riverine areas of the reservoir to the main basin. The TN:TP ratio went from 6.7 in the riverine zones to 14.2 in the main basin. The reservoir was eutrophic according to all the criteria assessed. Using growing season means for the main basin: chlorophyll a = 16 μg·L−1 > 10 μg·L−1, TP = 39 μg·L−1 >20 μg·L−1, TN = 0.52 mg·L−1 > 0.50 mg·L−1, Secchi disk depth = 1.13m < 2 m. Practices aimed at reducing phosphorus and sediment loadings are suggested to improve water quality.
12 citations
TL;DR: Aquashade™, a colorant and dye registered by the US Environmental Protection Agency (USEPA) for use in aquatic environments to manage plant growth, does not reduce the visibility of water that otherwise would meet safe swimmming standards.
Abstract: Aquashade™, a colorant and dye registered by the US Environmental Protection Agency (USEPA) for use in aquatic environments to manage plant growth, does not reduce the visibility of water that otherwise would meet safe swimmming standards. This product was examined for its potential impact on underwater visibility in surface waters used for recreational swimming. Aquashade™ treatments of 0, 1, and 5 mg L−1 were evaluated in 3-m deep outdoor tanks containing reservoir water. Transparency and light attenuation were examined using a Secchi disk and an underwater photo synthetically active radiation (PAR) meter. In the first experiment, filtered lake water was used, while in the second, bentonite clay was added to provide a light transparency of approximately 1 m. In filtered lake water, Aquashade™ treatments (1 mg L−1 and 5 mg L−1) reduced light transparency by approximately 10% and 30%, respectively, but the transparency (272 and 194 cm, respectively) was well above typical international (100 cm) a...
8 citations
01 Jan 1999
TL;DR: A review of the hydro-optical studies in the Black Sea from 1922 till now is presented in this article, where seasonal and long-term variability of the black sea optical parameters are analyzed using data sets from the data bases of Marine Hydrophysical Institute (Ukraine) and Institute of Marine Sciences (Turkey).
Abstract: A review of the hydro-optical studies in the Black Sea from 1922 till now is presented. Seasonal and long-term variability of the Black Sea optical parameters are analysed using data sets from the data bases of Marine Hydrophysical Institute (Ukraine) and Institute of Marine Sciences (Turkey). A dramatic decrease in the water transparency was observed during 1986–1992. This coincided with significant changes of the spectral distribution of optical parameters. The main reasons of such changes are eutrophication, influence of the biological invader Mnemiopsis leidyi on the sea ecosystem, and the natural 11 year solar cycle.
6 citations
Journal Article•
TL;DR: Deepest transmission of light in water and relatively low fluorometer values were found in the western areas of the lake, where light (at 1% level of surface radiation) was transmitted more than six metres.
Abstract: A fluorometer and multispectral underwater photodetector was used in different parts of Lake Ladoga during a joint Russian-Finnish expedition in 1995 to measure in vivo fluorescence and the intensity of solar and sky radiation. The spectral distribution of radiation at various depths in the water column and penetration of photosynthetically active radiation (PAR ) were measured using an underwater multispectral photodetector (420-670 nm). The results were compared with Secchi disk and temperature measurements. The fluorometer values were highest in he pelagic zone of the lake and smallest in areas close to the Burnaya River and in the Volkhov Bay. Light absorption by algae and other suspended matter effectively reduced light penetration especially in the Volkhov Bay. Deepest transmission of light in water and relatively low fluorometer values were found in the western areas of the lake, where light (at 1% level of surface radiation) was transmitted more than six metres. Pulp mill waste waters seemed to decrease the photosynthetic activity in the NE part of the lake.
TL;DR: In this paper, the authors used a closed-ended viewer box in the measurement of Secchi depth and compared the results with simultaneous naked-eye measurements, showing that the difference between viewer box and naked eye measurements increases with increasing wave height but not with increasing illuminance.
Abstract: We used a closed-ended viewer box in the measurement of Secchi depth and compared the results with simultaneous naked-eye measurements. We have shown that use of such a viewer box increases Secchi depth measurement by removing the interfering effects of water surface glare and glitter. A viewer box also increases between-observer precision. Measurements made both with and without the viewer box are slightly greater on the shady side of the boat than on the sunny side; the latter is the preferred side if Secchi data are to be related to other optical properties. As expected, the difference between viewer box and naked eye measurements increases with increasing wave height but not with increasing illuminance. Because of the lack of uniformity in the way Secchi depth is estimated, and the inherent optical problems with current Secchi depth procedures, an appeal is made for production of a standardized protocol for Secchi observations, including the use of a closed-ended viewer box on the sunny side of the boat.