Management and Conservation of Freshwater Systems II
Presiding: J Harding, University of Canterbury; S Grubbs, Western Kentucky University
NB14C-01 15:30h
Where have all the caddis gone? The role of culverts, and spiders
Restoration of a 1.5 km urban stream over the past five years has led to surprisingly slow improvement in benthic communities. Analysis of benthic invertebrates at six sites longitudinally showed a marked decline in caddisfly diversity and abundance upstream. This decline could not be adequately explained by changes in water quality, or in-stream physical conditions. Extensive adult trapping on multiple sites on three urban streams has shown that main roads with culverts act as barriers to the upstream flight of adult caddisflies. When adult caddis encounter a road culvert, some are distracted by the surrounding urban conditions (e.g. street lights), and only 30-50% enter the culvert. Of these, about 10-30% do not reach the upstream exit falling prey to spiders or distracted by confounding flight cues. Experimental removal of spiders and webs from three culverts showed an increase in the proportion of caddis exiting upstream. Other confounding effects on caddisflies within the culvert might include light, humidity and temperature gradients. Our results indicate that barriers to adult dispersal and colonisation, such as road culverts and confusing urban habitats, may markedly limit the recovery of urban stream communities.
NB14C-02 15:45h
Stream Crayfish Distribution Patterns and Habitat Associations in northern Mississippi
Distribution patterns and habitat associations of crayfishes in Mississippi are largely unexplored. During summers 1999-2003, we sampled crayfishes, fishes and habitat in 119 stream sites in northern Mississippi. We captured over 1,200 crayfish of 9 species from 3 genera. Species co-occurrence analyses and principal components analyses (PCA) of species abundances indicated significant species structuring among crayfish assemblages. We infer from co-occurrence patterns that both competitive interactions and historic processes led to present distributions. Mantel tests and PCA both indicated that crayfish assemblage characteristics are significantly related to stream size, but not to other habitat variables. In contrast to the nearly-universal rule for aquatic taxa that species richness increases with stream size, crayfish richness, abundance, and density were inversely related to stream size. Crayfish densities dropped precipitously when watershed area exceeded about 2,500 hectares. The low richness and abundance of crayfishes in medium and large streams may be due, in part, to the extreme disturbance from channelization and incisement in middle to lower reaches of most of the drainages we studied. Intermittent and very small perennial streams are sometimes regarded as biologically unimportant by land managers, but are primary strongholds of stream crayfishes in northern Mississippi.
NB14C-03 16:00h
Spatially explicit mapping of potential benthic invertebrate assemblage classes using GIS
A spatially explicit classification of the biological potential of streams is desirable for conservation planning. Such a classification would allow land managers to identify and locate biologically important stream reaches for protection or restoration. Our ability to interpolate stream classes between sampled and unsampled reaches has been limited by the availability of spatial data and algorithms that can accurately estimate local environmental settings at an appropriate resolution. However, the availability of finer resolution digital elevation models is continually increasing along with the development of better algorithms for predicting environmental settings, such as channel slope and valley confinement by hillslopes. We classified a set of training reaches based on their benthic invertebrate assemblages. We then developed a discriminant functions model to predict biological class at other reaches from easily derived map variables, and applied the resulting model to rasterized stream networks within a GIS. We illustrate use of this technique for streams in several ecoregions.
NB14C-04 16:15h
Monitoring Freshwater Biodiversity at Large Scales: An Assessment of Potential Indicators
Conservation of freshwater biodiversity is a priority for both government agencies and national and international conservation organizations. A number of large-scale conservation plans specifically targeting freshwater biodiversity have been, or will soon be, implemented across the globe. Although numerous potential biodiversity indicators have been proposed for monitoring the status of freshwater ecosystems, few of these indicators have been evaluated. Choice of indicator is especially problematic in many parts of the developing world, where biodiversity data are sparse in general and budgets are limited. In contrast, many developed countries have created freshwater biological assessment programs, which are generally based on measuring aspects of macroinvertebrate assemblages. However, macroinvertebrate-based assessments have not been generally applied to biodiversity conservation, and the extent to which macroinvertebrate-based measures reflect trends or responses in other taxa is unclear. We reviewed the extensive biodiversity and bioassessment literature to identify a practical set of biodiversity indicators for monitoring the success of freshwater conservation plans. After defining the properties that such indicators should possess, we concluded that no single extant indicator can adequately assess the biodiversity status of freshwater fauna. We highlight areas for further research and suggest combinatorial approaches that may prove adequate in the interim.
NB14C-05 16:30h
The Influence of Climate Change on Sediment Retention by Riparian Buffers
During the last century, many parts of the U.S. experienced warming temperatures and increases in precipitation amount and intensity. Projections of future climate suggest these trends are likely to continue. Previous studies have illustrated potentially significant changes in soil erosion from agricultural fields under alternative climate conditions. Riparian buffers are widely applied to reduce sediment loading to streams, but their effectiveness will likely vary depending on buffer characteristics and on future climate. In this study, we link the WEPP and REMM hillslope-scale models to evaluate how different climate change scenarios could influence upland soil erosion and sediment retention by riparian buffers. Results suggest complex, non-linear relationships between changes in precipitation volume and intensity and resulting changes in upland erosion and sediment loading to streams. For example, in one test case, an 18% decrease in annual precipitation decreased sediment loading to a riparian buffer by 3%, but increased sediment loading to the stream by 11%. In a different case, doubling precipitation increased sediment loading to the buffer and stream by 1200% and 3900%, respectively. A quantitative understanding of these relationships will help watershed managers develop effective adaptation strategies to achieve sediment management goals over a range of time scales.
NB14C-06 16:45h
Factors influencing the distribution of lotic fish assemblages in the Upper Green River - Kentucky CREP region.
Streams are linked to their surrounding landscapes and water quality varies with respect to land use heterogeneity and disturbance frequency. Kentucky's Green River is one of the top four rivers in the U.S. according to fish (151 species) diversity. In 2001 the Upper Green River Basin was established as the geographic entity of Kentucky's U.S.D.A. Conservation Reserve Enhancement Program (CREP). The main goal of the Kentucky CREP is to reduce non-point source pollution loading by recruiting landowners into incentive-based cooperative agreements aimed to mitigate riparian-based agricultural and animal husbandry impacts. The intent of this study was to study spatial patterns of lotic fish assemblages in the Kentucky CREP-Upper Green River Basin as they relate to environmental parameters across three spatial scales (riparian, reach, and watershed). Stream segments were weakly grouped by an initial ordination analysis by stream size or subbasin location, except for numerous sites along the mainstem Upper Green River. A forward-selection CCA revealed that the stream-size gradient, and not % agriculture at any scale, was mainly responsible for the partitioning of fish assemblages. Significant variables elucidated were all related to stream size, namely mean summer temperature, watershed area, total suspended solid content, and dissolved oxygen.