Decomposition impacts carbon storage release in ecosystems and is often mediated by sodium availability. Sodium is limiting for terrestrial heterotrophs away from coastlines. However, human activity has increased inland salt levels through mining, road salting, and agriculture. Increased sodium can stimulate decomposition directly via detritivore access, or indirectly through increased plant sodium concentrations. Riparian systems are essential buffers to aquatic ecosystems and how rising salt levels impacts riparian processes is not well understood. To test the prediction that low-level sodium additions would increase decomposition rates and plant leaf sodium concentrations in a southeastern US riparian system, we delineated 20- 1 x 1 m plots alongside Wafer Creek (Ruston, LA). We randomly assigned 10 plots as salt (NaCl) treatments which received 500mg in 0.75 L H2O and 10 plots as controls, which received 0.75 L H2O. Plots were watered with their respective treatment every two weeks. We collected litterbags that initially had 3g of red maple leaves on days 0, 7, 21, 89, and 257. Additionally, we collected live leaves from three species of plants on plots for sodium content analysis at 6 and 9 months: ivy (Smilex pumila), sedge (Carex sp.), and river oaks (Quercus nigra).
Results/Conclusions
Leaves lost ~30% of their mass over 9 months. Decomposition rates did not significantly differ between low-level sodium plots and control plots, but trended for 21% slower decomposition on salt than control plots. Conversely, low-level sodium inputs had large effects on plants. At both 6 and 9 months, plants on salt plots had more salt than those on control plots. Ivy (S. pumila) contained ~1.4 times more salt, the sedge (Carex sp.) contained ~2 times more salt, and oak (Q. nigra) contained ~4.7 times more salt than conspecifics on the control plots after 9 months. Together these results suggest that low-level sodium additions may slow or have little direct effect on decomposition rates in riparian systems, but will alter sodium concentrations in a diversity of plant leaves. Slower decomposition rates may result from potential sodium toxicity to detritivores in riparian systems. Furthermore, salt is toxic to many plants, so the uptake of salts may negatively affect the general health of the plants, and abscised leaves with increased salts may result in longer retention of those salts in the soil and indirect negative effects on decomposition rates. These processes are likely to impact riparian input to stream ecosystems and ultimately stream ecosystem processes.