| dc.description.abstract | Atmospheric deposition of nutrients, mainly nitrogen and phosphorus can significantly affect aquatic ecosystems productivity, eutrophication, and biogeochemistry. Recent studies have suggested that atmospheric deposition constitute a significant source of nutrients to aquatic ecosystems. The purpose of this study was to improve an understanding of seasonal changes, sources and pathways of atmospheric nutrient depositions loading into Lake Kivu, DR Congo. The specific objectives of this study were to: (1) determine atmospheric nutrient, and major ions deposition under different land uses/covers in Lake Kivu basin in DR Congo side; (2) determine the origin of nutrients (P, N and C) loading in Lake Kivu via atmospheric deposition and (3) assess the effect of atmospheric deposition on multi-level nutrient content in Lake Kivu. Dry and wet atmospheric deposition samples were collected at four stations (Goma, Lwiro, Bukavu and Iko) in the Lake Kivu basin from four different land use/cover types. Three experiments were undertaken for 30 days to simulate the enrichment status of the lake from dry and wet atmospheric deposition. Samples were analysed for selected nutrients, major ions and isotopic composition. Data for wind speed (m/s) and direction (o) was collected using the automatic sensor at the Lwiro station during the study period. Results indicated that the highest annual loading of dry total phosphorus (TP; 4.4 ± 3.9 µmol/m2/yr) and dry total nitrogen (TN; 84.5 ± 41.2 µmol/m2/yr) were recorded in the forest land cover of Goma urban area, and in all the land use/cover types of Iko, respectively. The dominant anions in the wet deposition were SO4 2- and NO3 − , found around the rural area near the cement factory and the urban area near active volcanoes, respectively. The enrichment factors and correlation analysis indicated that the main sources of Ca2+, Na+ and Mg2+ were crusting processes, aeolian suspension of soil and volcanic ash, biomass burning and the cement/lime factory around the Lake Kivu watershed. The four stations' stable isotopic ratios of δ13C and δ15N in the dry and wet atmospheric deposition were significantly different (P<0.001). Natural and anthropogenic activities in the watershed, such as volcanic activities, biomass burning, and soil erosion, introduce particles in the atmosphere following meteorological conditions. Surface lake water becomes nutrient-rich due to increasing nutrient input. The major source of nutrients in the basin comes from the north part of the Lake (Goma) significantly contributing to Lake enrichment. Simulation of enrichment status shows that the addition of dry and wet atmospheric deposition caused a high TN: TP ratio. The wet atmospheric deposition had high effect on the nutrient ratio than dry atmospheric deposition (p > 0.05). The annual average concentration of nutrients deposited into Lake Kivu through both dry and wet atmospheric deposition has a greater impact on the nutrient ratio in the lake than the daily enrichment from atmospheric deposition alone. At the same time, the outflow simulated from River Ruzizi in the third scenario regulated the nutrient ratio of the water in the experiment. All levels of nutrient additions caused an increase in both Chl-a and DOC concentration (p < 0.05). This study found that forest traps high nutrient concentrations than other land uses/covers and can serve as a baseline for atmospheric nutrient loading sources in the Lake Kivu basin. Future studies on atmospheric nutrient deposition could provide more understanding to land managers for the management and protection of Lake Kivu. | en_US |
