摘要:

Using chlorophyll and phosphorus data from 119 Missouri reservoirs we show how data aggregation-averaging data into seasonal means or long-term lake means – influences our ability to make inferences from large-scale statistical regression analyses. We demonstrate the most obvious phenomenon of data aggregation, that relations between variables estimated from aggregated data are generally stronger than the same relations estimated from unaggregated data. Averaging reduces the often large variation in the response of chlorophyll to phosphorus (Chl-TP) that characterizes measurements of these variables in lakes. We also demonstrate that inferences made from statistical regression analyses apply only to situations that match the level of aggregation used to produce the model. Using lake means we found a strong positive Chl-TP relation. This strong cross-sectional pattern among lakes in the study, however, did not always reflect the relation of these variables to one another in individual lakes. And the cross-sectional pattern has limited value in predicting conditions in unaggregated data. The effect of aggregation on the estimated strength of a regression relation serves as a caution in transferring inferential statements about the effect of TP on Chi between temporal scales and among lakes.

ISSN:1040-2381    

DOI:10.1080/07438149809354104

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Water quality monitoring is invaluable to ensure compliance with regulations, detect trends or patterns, and advance ecological understanding. However, monitoring typically measures only a few characteristics in a small fraction of a large and complex system, and thus the information contained in monitoring data depends upon which features of the ecosystem are actually captured by the measurements. Difficulties arise when these data contain something other than intended, but this can be minimized if the purpose of the sampling is clear, and the sampling design, measurements, and data interpretations are all compatible with this purpose. The monitoring program and data interpretation must also be properly matched to the structure and functioning of the system. Obtaining this match is sometimes an iterative process that demands a close link between research and monitoring.

ISSN:1040-2381    

DOI:10.1080/07438149809354105

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The goals of the Lakes of Missouri Volunteer Program are to involve citizens in the collection of water samples to monitor lake trophic state and to provide outreach education about lake water quality. Results indicate data generated with volunteer help are of the same quality as that generated by a research laboratory. This conclusion is based on three different methods of evaluation: (1) Comparisons of volunteer and University collected samples showed trophic state classifications were the same for 74% of lakes based on total phosphorus, 84% for total nitrogen and 89% for chlorophyll; (2) Agreement between paired chlorophyll filters was assessed to gauge volunteer processing technique; 88% of the filter pairs was considered good or excellent based on a rating scale developed for this program; (3) Split sampling showed no significant differences for total suspended solids, chlorophyll or total nitrogen. Total phosphorus analysis showed a significant difference with volunteer samples being consistently less than University samples. Prior to analysis, volunteer samples for total phosphorus were stored frozen in high density polyethylene bottles while University samples were refrigerated in glass tubes. This difference in storage method may have caused the irregularity in our results.

ISSN:1040-2381    

DOI:10.1080/07438149809354106

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Selby Lake in Gates of the Arctic National Park and Preserve was assessed as oligotrophic due to measurements of low nutrient concentrations and resultant low planktonic biomass as total chlorophyll. An orthograde oxygen profile in early summer also indicated an oligotrophic condition. Total nitrogen averaged about 0.4 μg·L−1and total phosphorus about 4 μg·L−1, resulting in a TN:TP ratio of about 100, which indicated the planktonic algae were probably limited by phosphorus. Nutrient stimulation bioassays confirmed this. Nitrogen alone was not stimulating to plankton algal growth, but nitrogen and phosphorus added together in the bioassays stimulated growth more than just phosphorus, as is often found in oligotrophic lakes. Aerial observation of Selby Lake and similar nearby lakes had indicated that epilithic benthic algal biomass was probably relatively high because the extensive shallows were visibly green. When recent growth in the ice-scour zone (< 2 m) was sampled in early July, the whole lake average standing crop of epilithic algae was estimated as approximately equal to the whole lake standing crop of phytoplankton. Biomass was greater near inlets than away from inlets. Epilithic algal biomass varied inversely with the temperature of inlets and directly with the inlets' total nitrogen concentration. Root zone fixation of atmospheric nitrogen by alders may be the source of N in the enriched inlets, and cold inlets probably plunge to the lake bottom, bathing the epilithicalgae with nutrients. The importance of benthicalgae in clear-oligotrophic lakes with extensive shallows need to be recognized.

ISSN:1040-2381    

DOI:10.1080/07438149809354107

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Cladoceran zooplankton were collected and identified from spring and summer samples from vegetated and open water areas of 26 remnant glacial lakes in Dickinson County, Iowa. The purpose of the study was to determine the factors influencing the structure and composition of zooplankton assemblages as a tool for aiding environmental management of the region's prairie pothole wetlands and ponds. The ponds were assorted into five categories based on morphometric features and productivity: ‘chain lakes’ defined large, deep, interconnected lakes; ‘algal potholes’ were small pothole wetlands dominated by algal primary producers; ‘weedy potholes’ denoted similar ponds dominated by macrophytic vegetation; ‘sloughs’ were similarly dominated by macrophytes, but found along intermittent waterways subject to drying; and ‘walleye ponds’ were kettle-hole ponds modified for the production of gamefish. Multivariate analyses and similarity indices were used to determine the relationship between cladoceran assemblages and the five major lake types. Each lake type contained a distinct cladoceran assemblage that was influenced by the abundance of macrophytes and probably also by fish, although fish species composition was not directly measured. Cladoceran diversity also increased with increased predominance of macrophytes among lakes, and within the same lake in different seasons and sampling locations. A model was built to describe the relationship between cladoceran assemblages and macrophytes that could be used in management or paleoecological applications. If prairie potholes are to be managed for high invertebrate diversity to support waterfowl, our results promote plans that diversify benthic structure within ponds. Advanced eutrophication and conversion of existing potholes to game fish rearing ponds severely limit the abundance and composition of microcrustaceans, which is likely to alter upper levels of the food web.

ISSN:1040-2381    

DOI:10.1080/07438149809354108

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Inputs of total phosphorus (TP) to a small lake (0.4 km2) located in western suburban Boston were compared during a drought (fall 1995) and a normal rainfall period (fall 1994) to explore potential effects of Canada geese (Branta canadensis maxima) and climate change on phosphorus loading to suburban lakes of the Northeastern U.S.A. In fall 1994, the watershed supplied 18 times more TP than Canada geese, but during the fall drought of 1995, TP from Canada geese exceeded that from the watershed by more than 7 times. Differences in the relative importance of TP loading from Canada geese and the watershed were caused by variation in streamflow between years. Under conditions of climatic warming, annual streamflow in the Northeast (U.S.A.) is projected to decline by ~30% with greatest reductions (~60%) occurring in the fall. At this time of year, Canada geese are most abundant and are likely to become the major contributor of TP to urban lakes. Furthermore, annual absolute inputs of TP from geese to suburban and urban lakes of the Northeast are likely to increase with warmer conditions associated with climate change, because ice cover in winter is unlikely to form on lakes in this region. Consequently, geese are likely to remain on such lakes during the winter rather than moving to open coastal waters as they do presently when lakes freeze. Thus, both the warmer and drier conditions predicted to accompany climate change may exacerbate effects of Canada geese on the water quality of suburban-urban lakes in this region of North America.

ISSN:1040-2381    

DOI:10.1080/07438149809354109

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Florida lakes as a group exhibited a distinct seasonal pattern in the concentration of algal chlorophylls. This conclusion was based on an analysis of data from the Florida LAKEWATCH 1994 database containing 416 lake-years of observations from 209 lakes. For oligotrophic, mesotrophic, and eutrophic lakes, monthly chlorophyll concentrations were typically lower than the annual mean chlorophyll concentration from December to May and were higher from August to October. Hypereutrophic lakes (annual mean chlorophyll > 40 μg·L−1) tend to have high fluctuating levels of algal chlorophyll for most of the year except for low levels in December, January, and February. Maximum chlorophyll concentrations tended to occur most frequently from August to October, however the maximum or minimum level in any given lake can occur at any time of the year. The variance (s2) in monthly chlorophyll concentrations over the course of a year increased with increasing annual mean chlorophyll for Florida lakes. There was also seasonal variation in the monthly values for total phosphorus, total nitrogen, and Secchi disk transparency though the magnitude of the fluctuations was about half that for chlorophyll. They also showed increasing variance with increasing lake means. The 95% confidence limits for estimates of annual mean chlorophyll concentrations in these lakes with 12 monthly samples was ±27% of the mean. Similar confidence limits for means of total phosphorus, total nitrogen, and Secchi disk transparency were 15%, 9%, and 10%, respectively.

ISSN:1040-2381    

DOI:10.1080/07438149809354110

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The Eau Pleine Reservoir has historically experienced point and non-point source (NPS) pollution resulting in winter anoxic conditions and periodic fishkills. Because the reservoir has the potential to support a quality sport fishery, including walleye (Stizostedion vitreum) and northern pike (Esox lucius), minimizing the incidence of anoxic winter conditions is a management goal. During winter reservoir drawdown, a dissolved oxygen (DO) sag typically develops in the headwater and moves through the reservoir, leading to periodic fishkills. To identify factors that influence the DO sag and to determine if those factors could be managed, I evaluated historical fishkill records, winter DO data, river base flow (inflow), precipitation/runoff events, and reservoir operations data collected over a 24-year period. A combination of three key factors consistently affected the character (magnitude and duration) of the DO sag and the incidence of fishkills. No fishkills occurred when 1) reservoir volume at the start of winter drawdown was greater than 60%; 2) river base flow was 6 cfs or greater; and 3) the DO sag did not develop until after February 1.1 postulated that anoxic conditions during winter could be minimized by using these factors as guidelines for future reservoir operation, along with continued use of two aeration systems. Reservoir operating guidelines were developed and have been followed since 1993; no fishkills have occurred.

ISSN:1040-2381    

DOI:10.1080/07438149809354111

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Several water quality parameters, including inorganic nitrogens and phosphorus, were measured in groundwater from the Republican River aquifer above and below Milford Reservoir, Kansas. Ammonia and total phosphorus concentrations were considerably higher (>50%) in groundwater from the pressure relief wells along the toe of Milford Reservoir dam than from well water sampled upstream of the lake. However, the concentration of these compounds decreased to near upstream levels within 1.2 km downstream of the dam. Within the array of pressure relief wells, the concentration of ammonia was greatest in water from wells near the center of the dam. Conductivity, hardness, and alkalinity were lower, and pH was higher, in groundwater below Milford Reservoir than above it. The ratio of ammonia to total inorganic nitrogen in elutriates from Milford Reservoir sediments and water from the pressure relief wells was similar. These results suggest that water seeping out of reservoirs into underlying alluvial aquifers can leach soluble compounds, which exist in reservoir sediments, into the groundwater.

ISSN:1040-2381    

DOI:10.1080/07438149809354112

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Como Lake, a shallow hypereutrophic 29-ha lake, located in St. Paul, MN, was biomanipulated by fisheries renovation using rotenone in September 1985, to reduce algal standing crop, improve aesthetics, and increase recreational use. Long-term monitoring (1982–97) indicates a cyclic water quality and biologic response following the initial biomanipulation. Algal standing crop, as measured by chlorophylla(CHLA), varied positively with total phosphorus (TP) and total nitrogen (TN) for the post-biomanipulation years (1986–97), with marked changes in phytoplankton community composition and population abundance. Nutrient-phytoplankton (“bottom-up”) interactions are a strong and consistent force in Como Lake following biomanipulation due to continued high normalized areal phosphorus loading (~735 mg m−2yr−1). “Top-down” influences have not yet stabilized, but appear to have dampened with time due to decreased effectiveness of sportfishing regulations and fish stocking, along with partial winterkill due to aerator failure, to maintain piscivore abundance. Planktivorous fish abundance and size-selective feeding pressure on large-bodied herbivorous zooplankton grazers, as well as Daphnia biomass, have fluctuated cyclically over the study period. Recent decreased macrophyte abundance suggests a return to phytoplankton dominance as the long-term stable state for Como Lake. Monitoring results suggest that future management efforts in Como Lake should include renewed emphasis on fisheries and watershed management to promote the presence of macrophyte growth and a reduction in the magnitude of “bottom-up” forces, particularly nutrients, that effect the size of the algal population.

ISSN:1040-2381    

DOI:10.1080/07438149809354113

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor