Across-ecoregion analysis suggests a hierarchy of ecological filters that regulate recruitment of a globally invasive fish

Aim -- Even successful invaders are abundant only in a fraction of locales they inhabit. One of the main challenges in invasion ecology is explaining processes that drive these patterns. We investigated recruitment of a globally invasive fish, common carp (Cyprinus carpio), across three ecoregions to determine the role of environmental characteristics, predatory communities and propagule pressure on the invasion process at coarse and fine spatial scales. Location -- Lakes across Northern Forest, Temperate Forest and Great Plains ecoregions of North America. Methods -- We used data from 567 lakes to model presence or absence of carp recruitment using environmental conditions (lake clarity, area, maximum depth), native predatory fishes (micropredators, mesopredators, large predators) and propagule pressure (abundance of adult carp). We formed a set of alternative models and evaluated their support using an information theoretic approach. Once most supported models were identified, we used classification tree to determine how variables included in these models interacted to affect carp recruitment. Finally, we conducted a field experiment to test the predictions of the classification tree analysis. Results -- Carp recruitment was strongly regulated by processes associated with water clarity, which appeared to function as a broad-scale ecological filter. Carp were unlikely to recruit in clear, oligotrophic lakes (Secchi depth \u3e 2 m) despite the presence of adults in many such systems. Recruitment was more likely to occur in regions with turbid lakes, but abundant micropredators could inhibit it there. Main conclusions -- Carp recruitment and invasions across large geographic areas are attributable to a two-layer ecological filter with lake clarity/productivity acting as a coarse-scale filter and micropredators acting as a fine-scale filter. This two-layer filter might explain the complex patterns of carp invasions among and within different ecoregions. Ecological filters may also explain the success of other aquatic invaders that show similarly patchy spatial distribution patterns

Water quality is a poor predictor of recreational hotspots in England

Maintaining and improving water quality is key to the protection and restoration of aquatic ecosystems, which provide important benefits to society. In Europe, the Water Framework Directive (WFD) defines water quality based on a set of biological, hydro-morphological and chemical targets, and aims to reach good quality conditions in all river bodies by the year 2027. While recently it has been argued that achieving these goals will deliver and enhance ecosystem services, in particular recreational services, there is little empirical evidence demonstrating so. Here we test the hypothesis that good water quality is associated with increased utilization of recreational services, combining four surveys covering walking, boating, fishing and swimming visits, together with water quality data for all water bodies in eight River Basin Districts (RBDs) in England. We compared the percentage of visits in areas of good water quality to a set of null models accounting for population density, income, age distribution, travel distance, public access, and substitutability. We expect such association to be positive, at least for fishing (which relies on fish stocks) and swimming (with direct contact to water). We also test if these services have stronger association with water quality relative to boating and walking alongside rivers, canals or lakeshores. In only two of eight RBDs (Northumbria and Anglian) were both criteria met (positive association, strongest for fishing and swimming) when comparing to at least one of the null models. This conclusion is robust to variations in dataset size. Our study suggests that achieving the WFD water quality goals may not enhance recreational ecosystem services, and calls for further empirical research on the connection between water quality and ecosystem services

The application of a diatom-based transfer function to evaluate regional water-quality trends in Minnesota since 1970

Significant population growth over the last three decades, as well as efforts to improve surface-water quality mandated by the Clean Water Act, potentially have had opposing influences on aquatic ecosystems in the U.S. Because historical data on water-quality trends are limited over this time period, we developed a diatom-based transfer function to reconstruct chloride, color, acid neutralizing capacity (ANC), total phosphorus (TP), and pH in 55 Minnesota lakes. The lakes span three different ecoregions, as well as the Twin Cities metropolitan area, and differ in their history of settlement and land use, and in surficial geology, climate, and vegetation. Lakes in the Northern Lakes and Forest ecoregion are nearly pristine, whereas those in the other regions likely are strongly affected by urban or agricultural pollutants. Reconstructions of water-chemistry trends since 1970 suggest that recent human activities have had substantial impacts in both urban and rural areas. Chloride concentrations have increased in many Metro lakes, which may be due to road salts, and phosphorus levels have been steady or rising in agricultural regions. The majority of Metro lakes show some decline in TP, although many of the changes are not statistically significant based on our reconstruction techniques. There is no evidence that atmospheric deposition of sulfate or nitrate has caused acidification or changes in trophic state for remote lakes in the northeastern part of the state

The Regional Nature of Lake Water Quality Across Minnesota: An Analysis for Improving Resource Management

ABSTRACT-The diversity and number of lakes in Minnesota may be better understood by the use of regional characterizations of lake and watershed information. Recent efforts have utilized the ecoregion approach to define seven regions across Minnesota, four of which contain 98 percent of our lake resources. Typical land use patterns vary regionally as do lake water quality patterns. Understanding these patterns will assist lake managers to develop realistic goals and minimize false expectations. Regional assessments facilitate the definition of reasonable goals, expressed in terms of: average summer nutrient concentrations, probability of nuisance conditions ( e.g., estimates of algal bloom frequency), and probability of Secchi transparency ranges for lake resource management-for protective as well as restorative purposes. User perceptions of water quality also may be used to define swimmable conditions to assist in goal setting by lake resource managers

Natural Resources Research Institute Technical Report

Minnesota is divided into seven regions, referred to as ecoregions, as defined by soils, land surface form, natural vegetation and current land use. Since land use affects water quality, it has proven helpful to divide the state into regions where land use and water resources are similar. Data gathered from representative, minimally-impacted (reference) lakes within each ecoregion serve as a basis for comparing the water quality and characteristics of other lakes. Caribou, Grand, and Pike Lakes are located on the northern edge of the Duluth Metropolitan Area (Figure 1) in the Northern Lakes and Forests Ecoregion (Figure 2). Caribou Lake has an area of 569 acres (230 hectares), and a maximum depth of 21 feet (6.4 meters). The majority of the lake is less than 10 feet deep, and is dominated by emergent and submergent aquatic vegetation. Grand Lake has an area of 1742 acres (705 ha). Baby Grand Lake flows into Little Grand, which flows into Grand Lake. Similar to Caribou, much of Grand Lake (~ 95%) is less than 10 feet (3 m) deep, and vegetation dominates the shoreline and near-shore areas. Pike Lake has an area of 508 acres (206 ha), and is much deeper. The maximum depth is 60 feet (~18 m), and most of the lake is between 20-50 feet deep (6-15 m). These lakes all have relatively developed shorelines and are likely to experience increased development pressure in the next decade. They have also experienced some degree of water quality problems in the past. Efforts are underway to improve wastewater treatment on two of these lakes. Construction of a sanitary sewer was recently (1999) begun around Pike Lake, and a constructed wetland wastewater treatment system servicing a cluster of nine (9) lakeshore homes was installed at Grand Lake in late 1995. The present study was conducted because local units of government desired additional water quality information on these Duluth area lakes for planning purposes. The Pike Lake Association also desired some follow-up work for comparison to a previous MPCA study (Bauman 1994), and to better define current lake water quality prior to the installation of a sanitary sewer in the basin