Aquatic Macrophytes Alter Metabolism and Nutrient Cycling in Lowland Streams
Aquatic Macrophytes Alter Metabolism and Nutrient Cycling in Lowland Streams
复制标题
水生植物改变低地溪流的新陈代谢和养分循环
作者：
J. O’Brien;Joanna L. Lessard;D. Plew;S. Graham;A. McIntosh
大型植物影响着低地河流的物理、化学和生物学特性，因此在河流管理中可能是至关重要的。研究了三种低地农业河流中大型植物在调节代谢和养分循环中的作用。我们测量了生长季节和实验性大型植物去除后的溪流代谢，并使用磷酸盐和铵的短期营养添加来评估大型植物对养分吸收的影响。初级生产与植被盖度密切相关，且随着植被的去除而显著降低，而生态系统呼吸与植被盖度不相关，且不受植被去除的影响。磷素吸收速率与初级产量呈负相关，表明大型植物活性实际上减缓了磷素吸收。铵吸收与大型植物覆盖或代谢指标无关。溪流中的硝酸盐浓度通常超过流入的地下水浓度，这表明在这些以大型植物为主的溪流中，硝酸盐的净滞留量很少。大植物对磷的需要量比观测到的吸收率低10倍，表明大植物对磷的需要量远低于其他水系生物群。大型植物对氮的需要量与铵的吸收量基本相等，不足以影响高硝酸盐通量。这些结果表明，大型植物驱动生态系统代谢，但对水柱养分浓度的影响有限，因为大型植物的需求远远低于水柱的供应量。因此，我们河流中的大型植物对河流的营养状态有很大的影响，但通过管理影响营养物去除的潜力很小。
Macrophytes influence the physical, chemical, and biological characteristics of lowland streams, so may be critically important in stream management. We investigated the role of macrophytes in regulating metabolism and nutrient cycling in three lowland, agricultural streams. We measured stream metabolism over the growing season and following experimental macrophyte removal, and used short-term nutrient additions of phosphate (P) and ammonium to assess macrophyte influences on nutrient uptake. Primary production was closely correlated with macrophyte cover across all streams and dates, and decreased greatly with macrophyte removal, whereas ecosystem respiration was not correlated with macrophyte cover and was not altered by macrophyte removal. Phosphate uptake velocity was negatively related to primary production, suggesting that macrophyte activity actually slowed P uptake. Ammonium uptake was not correlated with macrophyte cover or metabolism metrics. Stream nitrate concentrations typically exceeded concentrations of incoming groundwater, suggesting little net nitrate retention in these macrophyte-dominated streams. Phosphorous demand by macrophytes was 10-fold lower than observed uptake rates, indicating that macrophyte P demand was much lower than that of other stream biota. Nitrogen demand by macrophytes was nearly equal to ammonium uptake and was not sufficient to affect the high nitrate flux. These results indicate that macrophytes drive ecosystem metabolism but have limited influence on water column nutrient concentrations because macrophyte demand is much lower than the supply available from the water column. Thus macrophytes in our streams had a large impact on stream trophic state, but offered little potential to influence nutrient removal via management.