Effects of in situ phosphorus enrichment on the benthos in a subalpine karst stream and implications for bioassessment in nature reserves

Park managers in nature reserves need scientifically defensible and operationally feasible ecological indicators to better manage protected areas for both nature conservation and tourism. Such needs are much more urgent in karst aquatic ecosystems where spectacular natural scenic wonders attract millions of visitors to natural areas with streams and lakes that are particularly vulnerable to nutrient pollution. To identify a set of biotic indicators of phosphorus (P) pollution in a karst stream, we conducted an in situ P enrichment experiment in a nearly pristine karst stream located at a UNESCO world heritage site in China. Our results show that both benthic algal assemblages and macroinvertebrates were sensitive to P enrichment. Changes in diatoms (e.g., Achnanthidium minutissimum, Delicata delicatula) and macroinvertebrates (e.g., collectors) were indicative of P enrichment. The color change of travertine bryophyte beds from creamy white to green was largely due to increase in filamentous green algae such as Zygnema sp., which may provide a visual cue for P enrichment and pollution. Our findings, in conjunction with further studies that directly link these indicators with human disturbance (e.g., tourist activities) throughout the park, could improve the operation of park managers in minimizing tourist-induced nutrient pollution and in operationalizing these indicators in the current environmental monitoring and assessment program.