Effects of the emergent macrophyte Juncus effusus L. on the chemical composition of interstitial water and bacterial productivity

Release of oxygen from the roots of aquatic macrophytes into anaerobic sedi ments can affect the quantity of interstitial dissolved organic matter and nutrients that are available to bacteria. Nutrient and dissolved organic ca rbon (DOC) concentrations were compared between subsurface (interstitial) w aters of unvegetated sediments and sediments among stands of the emergent h erbaceous macrophyte Juncus effusus L. in a lotic wetland ecosystem. Concen trations of inorganic nitrogen (NH4+, NO3-, and NO2-) were greater from sed iments of the unvegetated compared to the vegetated zone. DOC concentration s of interstitial waters were greater in sediments of the unvegetated zone both in the winter and spring compared to those from the vegetated zone. Al though DOC concentrations in hydrosoils collected from both zones increased from winter to spring, bacterial productivity per mg DOC in spring decreas ed compared to winter. Greater initial bacterial productivity occurred on D OM collected from the vegetated compared to the unvegetated zone in winter samples (days 1 and 4), with increased bacterial productivity on samples co llected from the unvegetated zone at the end of the study (day 20). Bacteri al productivity was significantly greater on all sampling days on DOM from vegetated samples compared to unvegetated samples. In nutrient enrichment e xperiments, bacterial productivity was significantly increased (p < 0.05) w ith phosphorus but not nitrogen only amendments.