Effects of agriculture, urbanization, and climate on water quality in the northernGreat Plains

Abstract

The Qu'Appelle Valley drainage system provides water to a third of the population of the Canadian Great Plains, yet is plagued by poor water quality, excess plant growth, and periodic fish kills. Fossil algae (diatoms, pigments) and invertebrates (chironomids) in Pasqua Lake were analyzed by variance partitioning analysis (VPA) to determine the relative importance of climate, resource use, and urbanization as controls of aquatic community composition . From fossil analyses, we identified three distinct biological assemblages in Pasqua Lake. Prior to agriculture (ca. 1776-1890), the lake was naturally eutrophic with abundant cyanobacterial carotenoids (myxoxanthophyll, aphanizophyll), eutrophic diatoms (Stephanodiscus niagarae, Aulacoseira granulata, Fragilaria capucina/bidens), and anoxia-tolerant chironomids (Chironomus). Principal components (PCA) and dissimilarity analyses demonstrated that diatom and chironomid communities did not vary significantly (P Ͼ 0.05) before European settlement. Communities changed rapidly during early land settlement (ca. 1890-1930) before forming a distinct assemblage ca. 1930-1960 characterized by elevated algal biomass (inferred as ␤-carotene), nuisance cyanobacteria, eutrophic Stephanodiscus hantzschii, and low abundance of deep-water zoobenthos. Recent fossil assemblages (1977)(1978)(1979)(1980)(1981)(1982)(1983)(1984)(1985)(1986)(1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994) were variable and indicated water quality had not improved despite 3-fold reduction in phosphorus from sewage. Comparison of fossil community change and continuous annual records of 83 environmental variables (1890-1994) using VPA captured 71-97% of variance in fossil composition using only 10-14 significant factors. Resource use (cropland area, livestock biomass) and urbanization (nitrogen in sewage) were stronger determinants of algal and chironomid community change than were climatic factors (temperature, evaporation, river discharge). Landscape analysis of inferred changes in past algal abundance (as ␤-carotene; ca. 1780-1994) indicated that urban impacts declined with distance from point sources and suggested that management strategies will vary with lake position within the catchment.

Spatial and temporal variability of prairie lake hydrology as revealed using stable isotopes of hydrogen and oxygen

“…All calculations were performed using CANOCO version 4 (ter Braak and Š milauer 1998). Further statistical details are provided in Hall et al (1999). We hypothesized that E : I ratios should increase as a function of lake water salinity due to evaporative concentration of dissolved salts and enrichment of heavy isotopes during summer.…”

“…Preliminary analysis of data using detrended correspondence analysis revealed the presence of short environmental gradients; therefore, redundancy analysis (RDA) was used to determine whether the amonglake variability in E : I and LEL distances could be explained by linear combinations of measured environmental predictor variables (Hall et al 1999). All variables were centered and standardized prior to analysis.…”

“…All variables were centered and standardized prior to analysis. Environmental variables included those parameters measured at all lakes at the time of isotope sampling (Table 1) and were included only if they were not collinear with other predictor variables (i.e., variance inflation factor ,20) and individually explained a significant (p , 0.05) amount of variation in E : I or distance to LEL (Hall et al 1999). Monte Carlo permutation tests with 999 iterations were used to determine significance of the first RDA axis.…”

Relationship between anthropogenic sewage discharge, marsh structure and bird assemblages in an SW Atlantic saltmarsh

“…The increase in the abundance of 323 seed-eater species, especially the Yellow-winged Blackbird, may result from the 324 increment in the spike density of S. alterniflora. Reductions in the abundance of benthic 325 infauna were observed close to a sewage output following an increase in sewage output 326 (Hall et al, 1999). Some benthic invertebrates, however, notably annelids, are abundant 327 close to sources of nutrient pollution (Green et al, 1990), favouring ground feeder birds.…”

“…The sewage discharge into the 370 Bahía Blanca estuary is being done without any treatment. In an advanced 371 eutrophication process, the production of high amount of detritus could be generating a 372 negative effect in marsh ecosystems (Hall et al, 1999) by several processes such as 373 decreasing the local or regional biodiversity, increased competitive advantage of 374 invasive species, loss of nutrient retention capacity or, shifts between "clear water" 375 macrophyte-dominated systems to turbid phytoplankton-dominated systems (see EPA,376 2008 for a review). The sewage effluent may also create conditions favoring parasites 377 on fishes and wading birds (Coyner et al, 2002(Coyner et al, , 2003.…”