Influence of Land Use Activities on Spatial and Temporal Variation of Nutrient Deposition in Mwanza Region: Implication to the Atmospheric Loading to the Lake Victoria

Abstract

Increase in population growth and the associated activities have increased the nutrient input to the Lake Victoria through atmosphere and river discharge. Atmospheric input of nutrient is believed to exceed that of river discharge due to relatively higher contribution of water mass to the Lake from atmosphere. However, precipitation characteristics with respect to nutrients have not been well studied to allow qualification and quantification of atmospheric contribution to the Lake Victoria. This study was conducted to investigate influence of land use activities on spatial and temporal variation of nutrient inputs from atmosphere and to estimate atmospheric loading to the Lake Victoria. The results revealed that there is significant spatial and temporal variation of nutrient deposition in the study area. High concentrations of nutrients were observed during short rains starting from September to December. This was attributed to dissolution of nutrients from soil particals and ash residues due to biomass burning accumulated in the atmosphere during dry season of June to August. Spatial variation of nutrients reflects land use activities. Urban and peri-urban areas showed very high concentration of nitrate nitrogen due to industrial and vehicle emission while rural area showed high concentration of phosphorous species and reduced forms of nitrogen species reflecting agricultural activities and animal keeping. Generally, nutrient deposition load was higher in rural area compared to urban with respective values of 15.5 and 13.9 kg·ha −1 ·y −1 for total nitrogen and 6.1 and 2.8 kg·ha·y −1 for total phosphorous. These results suggest that in order to realize significant reduction of nutrient input to the Lake Victoria, measures should be taken to control agricultural activities through proper land use planning. The measure may be directed to reduce biomass burning, emission from industries and vehicle as well as animal residue.

Nutrient release from sediments and biological nitrogen fixation: Advancing our understanding of eutrophication sources in Lake Victoria, Tanzania

“…Mwanza North Bay is under intensive anthropogenic nutrients release attributable to untreated discharges of industrial and domestic wastes and particulate matter direct into the lake via the Mirongo River. Further, the nearshore waters of the Mwanza municipality contain higher nutrient levels due to industrial and vehicle emission (Vuai et al., ). The present study indicated nutrient concentrations of 1,472.20 ± 97.52 μg TN L −1 hr −1 for total nitrogen and 143.69 ± 4.98 PO 4 ‐P L −1 hr −1 for total phosphate concentrations in Mwanza North Bay at the sediment–water interface attributed to the high level of anthropogenic activities in the area.…”

“…Similarly, Magu Bay is characterized by pollution from agriculture and animal husbandry practices, exhibiting high concentrations of NO 3 ‐N, TN, SRP and NH 4 + ‐N, compared to the pristine site. Previous studies identified agricultural and animal raising as the main contributors of total phosphorus load (Calamari et al., ), phosphorus species and reduced forms of nitrogen species (Vuai et al., ), with net nitrogen releases between 69% and 85% (Zhou et al., ). The nutrients from these sources are carried to the lake as runoff via the Simiyu River, resulting into high levels in the water column.…”

“…The estimated TP loadings are relatively comparable, being 5,693 t TP/year (COWI Consulting Engineers 2002) and 5,634 t/year (Scheren, 2003;Scheren et al, 1995Scheren et al, , 2000Scheren et al, , 2005. In the Mwanza municipality, Vuai, Ibembe, and Mungai (2013) recorded deposition rate of 15.5 and 13.9 kg ha −1 year −1 for total nitrogen and 6.1 and 2.8 kg ha −1 year −1 for total phosphorus. Muzuka, Machiwa, and Lugomela (2005) reported nitrogen accumulation in Magu Bay ranging from 0.51 to 4.37 g N m −2 year −1 , which led them to conclude that the bay was experiencing eutrophication problems.…”

Spatial and Long-Term Temporal Changes in Water Quality Dynamics of the Tonle Sap Ecosystem

“…The pH values and NO 3 − concentrations were similar across study sites of the TSE. This result is likely due to chemical constituents and buffering capacity of lake water, which has also occurred in the Lake Victoria [59]. The minimum pH value at each site ranged from 5.3 to 6.0 (Table S1).…”

A review of the socioecological causes and consequences of cyanobacterial blooms in Lake Victoria

“…Concerning the OL, it has been shown that in addition to river discharge, aerial depositions are the main source of nutrient inputs in the lake (e.g., Tamatamah et al, 2005;Kayombo & Jorgensen, 2006). Therefore, a reduction of these inputs would be associated with an integrated approach for the protection of the catchment area, including better soil cover management and improved land use patterns (Okungu & Opango, 2005;Vuai et al, 2013). To adequately protect the watershed, deforestation needs to be halted and forests need to be restored; this constitutes a much greater challenge due to the complexity of the drivers of this phenomenon (Masese et al, 2012;Waiswa et al, 2015).…”