Walter G. Duffy

Effects of sediment load on emergence of aquatic invertebrates and plants from wetland soil egg and seed banks

Intensive agricultural activities near prairie wetlands may result in excessive sediment loads, which may bury seed and invertebrate egg banks that are important for maintenance and cycling of biotic communities during wet/dry cycles. We evaluated effects of sediment burial on emergence of plants and invertebrates from seed and invertebrate egg banks. Sediment-load experiments, indicated that burial depths of 0.5 cm caused a 91.7% reduction in total seedling emergence and a 99.7% reduction in total invertebrate emergence. Results of our burial experiments corroborated prior research on seedling emergence. However, our study demonstrated that invertebrate emergence is also highly susceptible to the effects of burial. Our research suggests that sediment entering wetlands from agricultural erosion may also hamper successional changes throughout interannual climate cycles. Land-management strategies need to be implemented that will prevent erosion of cropland top soil from entering wetlands.

Caloric Densities of Three Predatory Fishes and Their Prey in Lake Oahe, South Dakota

ABSTRACT We determined mean seasonal caloric density of walleye Stizostedion vitreum, chinook salmon Oncorhynchus tschawytscha, rainbow trout Oncorhynchus mykiss and ten species of prey fish from Lake Oahe, South Dakota. Age 3 and older walleye, chinook salmon, and rainbow trout showed distinct seasonal patterns in mean caloric density during May through September, 1994. Energy content of these fish was lowest during spring and highest during fall. No seasonal pattern in mean caloric density of ages 1 and 2 walleye, chinook salmon, and rainbow trout was observed, but caloric content differed among months. Seasonal differences in caloric density were also observed for rainbow smelt Osmerus mordax, yellow perch Perca flavescens, spottail shiners Notropis hudsonius, and lake herring Coregonus artedi. This study demonstrated that age and season contribute to the variability in the energy content of fish from Lake Oahe. Life history stage and season should be considered in energetics studies of fishes.

Fidelity and Survival of Juvenile Coho Salmon in Response to a Flood

Abstract We compared the movement and spring out-migrant trap capture of 1,038 juvenile coho salmon Oncorhynchus kisutch tagged with passive integrated transponder (PIT) tags among four alcoves, seven backwaters, and six main-channel pool habitats after a 5-year flood. Sampling was conducted in November 1998 before the flood on 21 November and again in December, January, February, and March in selected habitat units. Along with out-migrant trapping during spring 1999, these repeated sampling efforts were used to measure the fidelity of juvenile coho salmon to particular habitat units, the immigration of coho salmon into those habitat units, and out-migration from them. Following the flood, fidelity and out-migrant trap capture were greater for juvenile coho salmon occupying alcoves (50% and 17.0%) than for those occupying backwaters (16% and 6.1%) or main-channel pools (7% and 2.7%). The out-migrant trap capture of juvenile coho salmon that had been PIT-tagged before the flood (16.1%; N = 209) was similar...

Aquatic invertebrate production in southeastern USA wetlands during winter and spring

We measured aquatic invertebrate abundance, standing stock biomass, and community production in three types of wetlands on Noxubee National Wildlife Refuge from December 1987 through April 1988. Together,Orthocyclops modestus andDaphnia pulex were the most abundant organisms collected in all habitats during both winter and spring, but each contributed little to total standing stock biomass or production.Caecidotea communis andPristina osborni made up ≥47% of the total standing stock biomass at each site during both winter (December–February) and spring (March–May).Crangonyx gracilis, Chironomus spp.,Chaoborus punctipennis, andEclipidrilus spp. each contributed ≥5% of the total biomass at one or more wetland habitats. Estimates of aquatic invertebrate community production ranged from 930 to 1,578 mg dry weight/m2 among wetland types during winter and from 3,306 to 5,421 mg dry weight/m2 among wetland types during spring.Caecidotea communis andPristina osborni contributed most to community production during both seasons, but particularly in beaver ponds during spring. Other taxa made up substantial portions of the community production in one or two wetland habitats.

A caloric-based evaluation of diet indices for largemouth bass

Selection of methods for quantitative description and assessment of food habits is a concern for trophic investigations. We used diet data for largemouth bass Micropterus salmoides, to compare a caloric-based approach with eight diet indices: percent frequency of occurrence, percent total number, percent total weight, mean relative number, mean relative volume, relative importance index, prey-importance index, and mean stomach fullness. Mean caloric contribution of stomach contents for each prey taxon was used as a standard to compare diet indices. Temporal differences in composition and caloric contents of largemouth bass stomach contents were apparent. Most diet indices provided similar assessments when diets were dominated by a single prey type (i.e., gizzard shad during June-October). However, diet indices evaluated provided dissimilar assessments of stomach contents when a variety of prey with differing caloric densities were consumed (e.g., April). Mean stomach fullness and percent by volume were significantly (p < 0.002) correlated (r = 0.94 − 1.00) with mean caloric contribution of largemouth bass stomach contents during all months. Unlike percent by weight, mean stomach fullness accounted for differences in fish size and stomach capacity. Thus, mean stomach fullness by prey type appears to be the most appropriate index when objectives include simplified caloric-based assessments of fish diets.

Integrating estimates of ecosystem services from conservation programs and practices into models for decision makers

Most government agencies involved in land management are seeking consistent approaches to evaluate the effects of specific management actions on ecological processes and concurrent changes on ecosystem services. This is especially true within the context of anthropogenic influences, such as land use and climate change. The Conservation Effects Assessment Project—Wetlands National Component (CEAP–Wetlands) was developed by the U.S. Department of Agriculture (USDA) to evaluate effects of conservation practices on ecosystem services including carbon sequestration for climate stability, groundwater recharge, runoff and flood attenuation, water storage, nutrient and contaminant retention, and wildlife habitat. A primary purpose of CEAP–Wetlands is to provide science-based information in an adaptive monitoring framework for use by the USDA to facilitate policy and management decisions, and to document effects of conservation programs and practices to the federal Office of Management and Budget. Herein, we propo...

Invertebrate egg banks of restored, natural, and drained wetlands in the Prairie Pothole Region of the United States

Analogous to ‘seed banks,’ ‘egg banks’ are important for seasonal succession and maintenance of invertebrate species diversity throughout wet and dry cycles in the prairie pothole region. Further, recruitment of invertebrates from relic egg banks in the sediments and dispersal of eggs into wetlands is believed to be important for reestablishment of invertebrates in recently restored wetlands. Although tens-of-thousands of wetlands have been restored in the prairie pothole region of the United States, studies have not been conducted to evaluate the recovery of invertebrate egg banks in restored wetlands. We used taxon richness and abundance as indicators of potential egg bank recovery and compared these parameters in restored wetlands to those of non-drained and drained wetlands with a history of cultivation and also to reference wetlands with no history of cultivation. We found few significant differences among wetland categories within three physiographic regions (Glaciated Plains, Missouri Coteau, and Prairie Coteau). Most statistical comparisons indicated that restored wetlands had invertebrate egg banks similar to reference, nondrained, and drained wetlands. The one exception was drained seasonal wetlands in the Glaciated Plains, which had significantly lower taxon richness and invertebrate abundance than the other wetland categories. Trends did suggest that invertebrate egg bank taxon richness and abundance are increasing in restored seasonal wetlands relative to their drained analogues, whereas a similar trend was not observed for restored semi-permanent wetlands. Although recovery was not related to years since restoration, comparisons of restored wetlands with reference wetlands suggest that recovery potential may be inversely related to the extent of wetland drainage and intensive agriculture that varies spatially in the prairie pothole region. Our research suggests that periodic drawdowns of semi-permanent restored wetlands may be needed to promote production and development of invertebrate egg banks. Inoculation of restored wetlands may also be needed in areas where extensive wetland drainage has resulted in fewer wetland habitats to provide sources of passively dispersed eggs to newly restored wetlands.

Evaluation of Four Wetland Aquatic Invertebrate Samplers and Four Sample Sorting Methods

ABSTRACT Four sampling devices commonly used to collect aquatic invertebrates in wetlands were evaluated for their for their ability to capture a sample representative of the community. We also evaluated four benthic macroinvertebrate sorting techniques for their efficiency in separating organisms from samples. Of the four sampling gears evaluated, two were considered active (Gerking and core samplers) and two were passive samplers (activity trap and artificial substrate). Sampling gear evaluations were based on the number and diversity of aquatic invertebrates captured. The Gerking sampler captured significantly (P = <0.0001) greater densities of aquatic invertebrates than core or artificial substrate samplers and slightly (P = 0.056) greater densities than activity traps. Fewer taxa (P < 0.0001) were recorded in core samples than in other sampling gears. Sorting techniques included two types of dye, an elutriator device, and a behavioral extraction device. Dyes were evaluated on the basis of time taken ...

Wetland ecosystem services in California's Central Valley and implications for the Wetland Reserve Program

Primary ecosystem services provided by freshwater wetlands in the California Central Valley, USA, include water quality improvement, biodiversity support, and flood storage capacity. We describe these services for freshwater marshes, vernal pools, and riparian wetlands and the implications for wetlands restored under USDA programs in the Central Valley. Californias Central Valley is a large sedimentary basin that was once covered by grasslands, extensive riparian forests, and freshwater marshes that today have been converted to one of the most intensive agricultural areas on earth. Remaining freshwater wetlands have been heavily altered, and most are intensively managed. Nitrogen loading from agriculture to surface and groundwater in the Central Valley was estimated to be 34.7 3 10 6 kg N/yr. Atmospheric deposition of nitrogen in the Central Valley was estimated to be 44.3 3 10 6 kg N/ yr, of which ;1.5 3 10 6 kg N/yr was introduced directly to wetlands. Our analysis indicates that wetlands enrolled in the USDA Wetland Reserve Program (WRP) may potentially denitrify the NO3-N load from relatively unpolluted source water in ,18 days, but the potential to denitrify the NO3-N load from highly polluted source water is uncertain. Water management strongly influences use, diversity, and abundance of avian fauna as well as other biota. Freshwater marshes in the region continue to support important populations of breeding and wintering waterfowl and shorebirds whose populations fluctuate seasonally. Avian diversity in the little remaining area of Central Valleys riparian wetlands is also high and influenced by stand maturity, heterogeneity, and diversity. USDA conservation practices that promote these characteristics may support avian diversity. Effects of USDA conservation practices on non-avian fauna are poorly understood and warrant further study.

Food Habits of Walleye in Shadehill Reservoir, South Dakota

ABSTRACT The growth rate of walleye (Stizostedion vitreum) in Shadehill Reservoir, a 1,900-ha impoundment in Northwestern South Dakota, is much slower than the statewide average. We investigated the food habits of walleye in Shadehill Reservoir from 1994 to 1995 to determine if the slow growth is prey-related. Walleye were collected at night using electrofishing equipment and experimental gill nets. Of the 201 stomachs examined, 114 contained food. We calculated the relative importance (RI) index to evaluate the contribution of each prey item to the diet. Due to a relatively small sample size and inherent gear biases, data from all seasons were combined and analyzed by length group. The RI analysis indicated that Daphnia spp. was the most important prey for sub-stock length (<25 cm total length) walleye. White bass (Morone chrysops) became increasingly important for longer walleye and was the most important prey for quality- to preferred-length walleyes (38–50 cm TL). Aquatic dipteran larvae were the seco...