Benthic community structure response to flow dynamics in tropical island and temperate continental streams.

摘要

Hydraulic characteristics in lotic ecosystems are influential in the structure and function of aquatic benthic communities. Human activities and the increased demand for freshwater have caused the modification of natural flow regimes worldwide. Hydrological alterations, such as dams, diversions, and channelizations, are associated with ecological change and known to have detrimental effects on benthic communities. As a whole, this dissertation investigated the effects of hydraulic variables on the spatial distribution of macroinvertebrates and habitat template characteristics in tropical and temperate freshwater streams of the West Maui Mountains, Maui, Hawaii, and in Dayton, Ohio.;The first two studies took place in Hawaiian mountain streams that have been diverted, often removing >95% of base flow, for development, agriculture and tourism, thus modifying the natural flow and altering habitat and species composition. A transplant study investigated the effects of water removal and increased density on dispersal and upstream migration of N. granosa. Initial mean upstream migration rate was 0.25, 0.66 and 1.16 m/d under reduced flow, natural flow and natural flow with increased snail density, respectively. Through calculations using rates from published studies of neritids migrating en masse or in long lines, we generated realistic time frames for N. granosa to migrate above diversions, ranging from 72 days to 2.5 years (aggregate) and 29 days to 1.1 years (long narrow line). By understanding upstream migration, recommendations for migratory pathway and population restoration can be applied globally for tropical amphidromous species.;Secondly, habitat template, discharge, habitat flow, and macroinvertebrate insect indices were evaluated within riffle and cascade microhabitats upstream and downstream of the highest elevation diversion in four streams of the West Maui Mountains. A significant 44% reduction in macroinvertebrate density downstream of diversions was found when streams and sites were pooled (p = 0.0009, df = 1, F = 11.49). Microhabitat had a significant effect on the ratio of native to introduced taxa densities, with the amphibious splash zone home to significantly more endemic taxa compared to riffles. Non-native taxa were dominant (> 95% by density) and ubiquitous in riffle habitats. Our findings contribute to ongoing water management and restoration efforts focused on the conservation of native species and habitat integrity in tropical streams worldwide.;Finally, in the Little Miami River, Ohio, the physical template and macroinvertebrate community were compared between riffle and run habitats. Mean flow velocity and macroinvertebrate densities were significantly greater in riffle (Flow: mean +/- SE = 0.74 +/- 0.04 m/s; Density: 1892 +/- 200.2) than run (Flow: 0.32 +/- 0.01 m/s; Density: 540.3 +/- 76.8) habitats. Linear regression found a positive and significant relationship (y = 4097x -- 115.1, p < 0.0001) where 49% of variation in macroinvertebrate density was explained by mid-column velocity. Our results call for the need of future analyses using simple and complex hydraulic variables to accurately predict the distribution of invertebrate communities.;In conclusion, comprehensive understanding of how flow variation affects stream ecosystems is necessary for the development of future management practices that promote balance between economic and environmental benefits.