Julie K. H. Zimmerman

Multifunctional Agriculture in the United States

Abstract We evaluated possible changes to current farming practices in two Minnesota watersheds to provide insight into how farm policy might affect environmental, social, and economic outcomes. Watershed residents helped develop four scenarios to evaluate alternative future trends in agricultural management and to project potential economic and environmental outcomes. We found that environmental and economic benefits can be attained through changes in agricultural land management without increasing public costs. The magnitude of these benefits depends on the magnitude of changes to agricultural practices. Environmental benefits include improved water quality, healthier fish, increased carbon sequestration, and decreased greenhouse gas emissions, while economic benefits include social capital formation, greater farm profitability, and avoided costs. Policy transitions that emphasize functions of agriculture in addition to food production are crucial for creating change. We suggest that redirecting farm payments by using alternative incentives could lead to substantial environmental changes at little or no extra cost to the taxpayer.

Effects of stream enclosures on drifting invertebrates and fish growth

Abstract Stream ecologists often use enclosure experiments to investigate predator–prey interactions and competition within and among fish species. The design of enclosures, manipulation of species densities, and method of replication may influence experimental results. We designed an experiment with enclosure cages (1 m2, 6-mm mesh) to examine the relative influence of fish size, density, and prey availability on growth of brown trout (Salmo trutta), brook trout (Salvelinus fontinalis), and slimy sculpin (Cottus cognatus) within enclosures in Valley Creek, Minnesota. In addition, we examined water flow and invertebrate drift entering enclosures and in open riffles to investigate whether enclosures reduced the supply of invertebrate prey. Growth of small (age-0) brook and brown trout was not influenced by fish density, but growth of larger (age-1) trout generally decreased as density increased. Sculpin growth was not related to fish size or density, but increased with mean size of invertebrates in the drift. Enclosures reduced water flow and tended to reduce invertebrate drift rate, although total drift rate (ind./min), total drift density (ind./m3), and mean size of invertebrates were not significantly different inside enclosures compared to adjacent stream riffles. Enclosures had no effect on drift rate or size of Gammarus pseudolimnaeus, the main prey item for trout and sculpin in Valley Creek. Overall, our analyses indicated that reductions of prey availability by enclosures did not influence fish growth. Trout growth may have been limited at larger sizes and densities because of increased activity costs of establishing and defending territories, whereas sculpin growth was related to availability of large prey, a factor not influenced by enclosures.

Distribution of juvenile crabs ( Epilobocera sinuatifrons ) in two Puerto Rican headwater streams: Effects of pool morphology and past land-use legacies

Headwater streams in the Luquillo Mountains of Puerto Rico support eight species of omnivorous freshwater decapods. One of the most abundant predatory deca- pods is the freshwater crab, Epilobocera sinuatifrons . We studied the distribution and pool-habitat occupancy of juvenile E. sinuatifrons in two headwater streams located in the Forest Dynamics Plot of the Luquillo Long Term Ecological Research Site in north- eastern Puerto Rico. We compared crab distributions along Quebrada Toronja, which was bordered by pasture more than 80 years ago, to distributions along a second stream, Quebrada Prieta, where the forest has remained intact and past disturbance was minimal. We tested the hypothesis that a legacy of past land-use had sufficiently modified the stream channel substrata and riparian forests along the Quebrada Toronja to the extent that juvenile crab abundance and habitat preferences would be affected. We selected nine study pools along 300m of Quebrada Prieta and eleven pools along 300m of Quebrada Toronja, and periodically sampled each pool for juvenile crabs as well as physical habitat (water depth, volume, velocity and substrate characteristics). Juvenile crabs were abun- dant in all pools, but were more abundant along the Prieta, which also had greater varia- tion in pool habitat compared to Toronja. Crab abundance in Prieta pools was correlated with higher water velocity and large substrate (boulders and rocks), whereas crabs in the Toronja were correlated with higher flows. This is the first report of habitat-specific dis- tributions of neotropical freshwater crabs in response to past land uses.

Interactions between Slimy Sculpin and Trout: Slimy Sculpin Growth and Diet in Relation to Native and Nonnative Trout

Abstract To investigate whether introductions of nonnative trout affect growth and diet of nongame fish in small streams, we designed a field experiment to examine interactions between slimy sculpin Cottus cognatus and native brook trout Salvelinus fontinalis or nonnative brown trout Salmo trutta. We hypothesized that brown trout would compete with and reduce growth of slimy sculpin. We expected no change in slimy sculpin growth in treatments with brook trout because the two species co-occur in their native range and thus may have evolved methods to partition resources and decrease competitive interactions. Enclosures (1 m2) were stocked with (1) juvenile brown trout and slimy sculpin, (2) juvenile brook trout and slimy sculpin, or (3) slimy sculpin alone (control). Fish were stocked at three densities to examine intraspecific versus interspecific competition. Replicates of each treatment were placed in riffles in Valley Creek, Minnesota, and six experimental trials were conducted over three summers (2002...

Prey Selection by Trout in a Spring-Fed Stream: Terrestrial Versus Aquatic Invertebrates

ABSTRACT We evaluated the prey sources that contributed to the diets of brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) in Valley Creek, Minnesota during the summer of 2003. We collected drift before dawn and in the afternoon on five dates in June, July, and August 2003 in three sequential riffles. Immediately following drift sampling, we collected brown and rainbow trout, 13–20 cm in length, in pools immediately below the riffles where drift was collected. Terrestrial invertebrates numerically comprised about 3% of the drift across times and dates but made up approximately 10% by number of the overall diet of brown and rainbow trout. Trout were size-selective, preferring larger invertebrates by both length (7.0–12.9 mm) and biomass. Gammarus pseudolimnaeus made up about 75% of the diet of brown trout and about 60% of the diet of rainbow trout based on biomass. Diet overlap was >60% for both trout in relation to total individuals, length, and biomass of invertebrate prey.

Do Conservation Practices and Programs Benefit the Intended Resource Concern

Many conservation programs under the 2002 Farm Act address resource concerns such as water quality and aquatic communities in streams. Analyzing two such programs, simulated changes in agricultural practices decreased field-edge sediment losses by 25–31% in two geophysically distinct Minnesota watersheds. However, while in-stream sediment concentrations and lethal fisheries events decreased significantly in one watershed, there was no discernable improvement for the fisheries in the other, despite potentially spending over

Land use, spatial scale, and stream systems : Lessons from an agricultural region

100,000 annually in conservation payments. These results highlight the importance of performance-based conservation payments targeted to genuine resource concerns in watersheds and the value of integrated bioeconomic modeling of conservation programs.