EFFECTS OF AN ENGINEERED FLOW DISTURBANCE ON MEIOFAUNA IN A NORTH TEXAS PRAIRIE STREAM

We studied the effects of an engineered flow disturbance on meiofauna (45-500 mu m) in an intermittent north Texas prairie stream. As part of an interbasin water-transfer project, water is being diverted by a pipeline across a catchment boundary and released into the headwaters of a natural stream channel. An initial test of the system provided an opportunity for controlled study of flow disturbance (extended near-bankfull discharge) in the stream. Quantitative meiofaunal samples were taken from sediments and small woody debris (<3 cm diam.) at two disturbed sites and one undisturbed site before and after a 2-wk water diversion. Before diversion, meiofaunal density was stable or increasing on both kinds of substrata at all sites. Meiofaunal density in sediments ranged from 15 to 699 per 10 cm(2), and density on wood ranged from 22 to 224 per 10 cm(2). In the sediment, nematodes, copepods, and rotifers accounted for 85-99% of individuals. Wood supported a more variable community; however, chironomids, nematodes, and rotifers accounted for 80-92% of individuals. Following water diversion, total meiofaunal density was reduced on both substrata at disturbed sites. In sediments, total density was reduced to 1-2% of prediversion levels and ail meiofaunal taxa were affected. On wood, total density was reduced to 10-17% of prediversion levels. Density of chironomids on wood at both disturbed sites and of nematodes at one disturbed site were unaffected. At the undisturbed site, meiofaunal density on both substrates remained stable or increased during the same period. Wood meiofauna were more resistant to flow disturbance than those in sediments and, one month after water diversion, greater recovery was observed on wood than in sediments at disturbed sites. Rotifers responded more rapidly than other major taxa, particularly on wood surfaces. It appears that small woody debris may be an important refuge and source of recolonization of meiofauna in streams after flooding.