Stream recovery from agriculture in the southern Appalachians.

Stream recovery from agriculture in the southern Appalachians is being studied by selecting stream sampling locations in agriculture, forests, and reforested agriculture. At each site, we plan to measure wood breakdown, microbial biofilm respiration, macroinvertebrate diversity, and ecosystem metabolism (primary production and respiration). Site Description: 5 streams in 6 land use categories: 1) Long-term forest 2) Long-term light agriculture 3) Long-term moderate agriculture 4) Long-term heavy agriculture 5) Reforested from moderate agriculture to forest 6) Reforested from heavy agriculture to moderate/light agriculture Wood Breakdown/Microbial Biofilm Respiration: 35 white oak veneers will be placed in each stream during winter 2001. Collect them semi-monthly and measure mass lost over time (decomposition) and respiration by microbes that have colonized the wood veneers. Macroinvertebrate Collection: Quantitative benthic samples of macroinvertebrates will be collected from each stream during spring 2001. Samples will be sorted and identified to measure assemblage structure and function. Ecosystem Metabolism: Ecosystem

metabolism will be measured during summer 2001 in each stream using upstream-downstream diurnal oxygen curve analysis. Reaeration will be measured by injecting a conservative tracer (Cl or Br) and volatile gas (sulfur hexafluoride, SF6) to quantify gas evolution over a 1-h travel time distance. Chemical/Physical Properties: Water chemistry will be measured in grab samples. Physical parameters include suspended solids, substrate size classification, and sediment properties (transport and deposition).

本研究针对阿巴拉契亚南部农业干扰后的河流生态恢复展开，选取农业用地、原生林地以及退耕还林区域内的河流作为采样位点。在每个采样位点，我们将测定木质碎屑分解、微生物生物膜呼吸作用、大型无脊椎动物多样性以及生态系统代谢（包括初级生产与呼吸作用）。
采样位点说明：本次研究覆盖6类土地利用类型下的5条河流：1) 长期原生林地；2) 长期轻度农用；3) 长期中度农用；4) 长期重度农用；5) 由中度农用土地复转为林地；6) 由重度农用土地复转为中度/轻度农用土地。
木质碎屑分解/微生物生物膜呼吸作用：2001年冬季，我们将在每条河流中放置35块白橡木薄板。后续每两周进行一次采样，测定薄板随时间推移的质量损失（即分解过程）以及定植于薄板表面的微生物的呼吸速率。
大型无脊椎动物采集：2001年春季，我们将从每条河流中采集定量底栖大型无脊椎动物样本。对样本进行分选与物种鉴定，以分析其群落结构与功能。
生态系统代谢：2001年夏季，我们将采用上下游昼夜氧曲线分析法，对每条河流的生态系统代谢进行测定。复氧速率将通过注入保守性示踪剂（氯（Cl）或溴（Br））与挥发性气体六氟化硫（sulfur hexafluoride, SF6），在1小时的水流迁移距离内进行量化测定。
化学与物理性质：通过瞬时取水样本测定水体化学性质。物理参数包括悬浮固体含量、底质粒径分级以及沉积物的迁移与沉积特性。