Carl Richards

Evaluating the influence of landform, surficial geology, and land use on streams using hydrologic simulation modeling

Abstract.Land use and geology are two important extrinsic factors regulating the structure and function of stream ecosystems. The interactions among these two landscape-scale factors on streams are, however, poorly understood. To determine the effects of these factors on stream flow, sediment, and nutrients, we analyzed 72 ungaged, agricultural watersheds in Minnesota and Michigan using the hydrologic model SWAT (the Soil Water Assessment Tool). The watersheds differed in surficial geology (landform) and land use, but were of similar size, with streams ranging from 2nd to 3rd order. SWAT was developed for use on ungaged basins, but to improve the outputs we used US Geological Survey discharge data from sites near our study watersheds for calibration. We found seasonal and annual differences in flow and nutrient and sediment loading across different land forms and land use types. Watersheds with greater amounts of row-crop agriculture and watersheds dominated by morainal landforms were associated with more sediment and nutrients and greater flow volumes and flashiness. Multivariate analyses identified at least nine landscape variables which were related to nutrients, sediment, and flow, although the responses varied between Minnesota and Michigan. Results also indicated the possibility of a threshold effect for row crop agricultural. Increases in this land use had little additional effect on nutrients or flow when percent row crop exceeds the threshold value. At moderate to high levels of row crop agriculture, watersheds appeared to show greater sensitivity to differences in landform.

Evaluating methods for assessing sediment quality in a Great Lakes embayment

A probability-based, sediment quality assessment was conducted during 1995 in the lower St. Louis River Area of Concern, located in western Lake Superior. A regional application of the intensified sampling grid developed for the United States Environmental Protection Agencys Environmental Monitoring and Assessment Program was used to randomly select 90 sites for measuring the following sediment quality indicators: sediment chemistry, physical parameters, sediment toxicity, and benthic macroinvertebrate community structure. Screening methods were used to assess sediment chemistry and sediment toxicity at all sites, whereas more conventional metrics were used at a subset of sites. In addition, sediment quality data were collected from 20 a priori training sites, 10 in low impact areas and 10 in high impact areas. Mean probable effect concentration quotients were calculated for sediment chemistry variables at each site. As the range of mean probable effect concentration quotients values increased, the incidence of sediment toxicity increased. Benthic data from the training sites were used to establish standard criteria for developing two benthic integrity indices based on multimetric analysis and discriminant function analysis. Based on the training site results, the discriminant function analysis categorized the macroinvertebrate community at all random sites as 45 percent low impact and 55 percent high impact. A multimetric approach categorized 55 percent of the random sites as low impact and 36 percent as high impact. Due to the overlap of 95 percent confidence intervals, the multimetric approach also placed 9 percent of the random sites into an indeterminate category. The incidence of high impact sites appears to be primarily due to physical habitat characteristics. This finding was supported by the sediment quality triad assessment of 52 random sites that indicated alteration of the benthic community at 71 percent of sites was probably not due to chemical contamination.

The geomorphic—trophic hypothesis for arctic lake food webs

We merged the concepts of predator control of trophic structure and biogeographic constraints on fish distribution in to a Geomorphic-Trophic Hypothesis (GTH) for a regionally defined group of arctic lakes. The GTH describes how landscape characteristics indirectly control lake food webs. Pur simply, because landscape criteria control the distribution of fishes, and fish can comrol lake trophic structure, the landscape, therefore, can indirecdy controllake trophic structure. In arctic Alaskan lakes, lake trout (Salvelinus namaycush) serve as keystone predators in large lakes of the region, dramatically affecting the structure of the benthic and pelagic communities. Lake trout lakes have a benthic community with significandy higher chironomid density, biomass, richness and H diversity compared to ponds or lakes containing other fishes (GüYKE & HERSHEY 1992). As an intermediate predator, slimy seu! p in ( Cottus cognatus) control the abundance, biomass and species diversity of larval chironomids on bare sediments (HERSHEY 1985), the dominant habitat in virtually alllakes in the region. Lake trout alter sculpin distribution, crowding them onto rocky and rock-mud interface refugia where there is less food (McDoNALD et al. 1982, HANSON et al. 1992). Lake trout predation also controls the size and habitat distribution of the large snail Lymnaea elodes, which in turn control the recruitment of the subdominant snail Valvata lewisi through competitive interactions (HERSHEY 1990, 1992, MERRICK et al. 1991). Large lake trout force arctic grayling ( Thymallus arcticus) and juvenile and young-of-year (YOY) lake trout into nearshore habitats where predation risk is low, but food availability and growth are also very low QoHNSON 1972, 1976, McDoNALD & HERSHEY 1992, McDoNALD et al. 1992, 1996). This is illustrated by the observation that when arctic grayling occur in lakes without lake trout, the large zooplankter Daphnia middendorffiana is absent. Such lakes have small-bodied, grazing zooplankton, including Daphnia longiremis and Bosmina longirostris (OBRIEN et al. 1979). Furthermore, the other common large zooplankter, Heterocope septentrionalis, is also often absent when lake trout are absent, but if present, is much smaller (mean 2.05 mm ± 0.15 S.E.) than in the lakes with both lake trout and grayling (mean 2.54 mm ± 0.089 S.E.) (OBRIEN unpublished). Thus, grayling can structure the zooplankton community to one that is small-bodied. However, this ability is gready reduced when grayling occur with lake trout. Because they serve as keystone predators, the ability to predict the distribution of lake trout is fundamental to predicting trophic structure. By quantifYing the landscape criteria for distribution of fishes, the geomorphic-trophic hypothesis serves as a predictive model for lake trophic structure. The objectives o f this article are to describe the GTH o f landscape control of fish distributions, and illustrate a test o f the GTH for lake trout.

Simulating effects of landscape composition and structure on stream water quality in forested watersheds

(2001). Simulating effects of landscape composition and structure on stream water quality in forested watersheds. SIL Proceedings, 1922-2010: Vol. 27, No. 6, pp. 3561-3565.