Major Ions in Atmospheric Deposition in Lake Kivu Basin

This study investigated the major ion composition and sources in wet and dry deposition samples collected over 15 months (December 2017 to February 2019) at four stations representing four different land use/cover types on the western side of Lake Kivu basin in D.R. Congo. The samples were collected every 13 days for dry deposition and two to three times per month for wet deposition. Samples were analyzed for major ionic components (Cl-, NO-3, SO2-4, Na+, K+, NH+4, Ca2+, CO2-3, HCO-3 and Mg2+). Electrical conductivity and pH were analyzed immediately in the field while major ion measurements were in the laboratory. Results showed the pH of both the dry and the wet depositions were higher than what would have been expected based on equilibration with atmospheric CO2 (pH > 5.6) at all four sites, with conductivity less than 50 μS/cm. The neutralization process in dry and wet atmospheric deposition is due to Ca2+, NH+4, HCO-3 and CO2-3. The anion: cation ratio in dry deposition was close to 1 for Iko and Bukavu, and it was greater than 1.0 (1.1 - 1.2) for Lwiro and Goma in wet deposition. The dominant anions in wet deposition were SO2-4 and NO-3, found around the rural area near cement factory and the urban area near active volcanoes, respectively. The most abundant cation was Na+ followed by K+. The enrichment factors and correlation analysis suggest that the main sources of Ca2+, Na+ and Mg2+ were disintegration of soil processes, aeolian suspension of soil and volcanic ash, biomass burning and the cement/lime factory around the Lake Kivu basin.

Growth and Development of <i>Cyperus papyrus</i>in a Tropical Wetland

Relative growth rate (RGR) is an important parameter in plant growth models. However, no field measurements of RGR have been made in Cyperus papyrus (papyrus) wetlands. In this study, the growth dynamics of aerial shoots were investigated in a tropical papyrus wetland. The aim was to estimate temporal changes in the growth rates, and also establish the effect of water level and temperature change on total culm number, culm recruitment and senescence. Dry weights of shoots during their life cycle were determined using a non-destructive method after establishment of relationship between culm diameter and dry weight. Measurements were made over period of seven months. During the course of the measurements, culm density significantly increased from 16.1 to 35.9 culms.m-2. There were significant changes in both culm recruitment and senescence. Maximum RGR of developing culms was 1.04 g g-1 d-1. Using a culm density of 27 per m-2, productivity range was 16.74 to 37.37 g m-2 d-1. There was an inverse and significant relationship between rate of change in leaf weight ratio (LWR) and RGR of the culms. In conclusion, RGR of the aerial shoot development was controlled by rate of change in LWR from 41 to 156 days of growth. There was a strong and negative influence of water level fluctuation on total culm density.

Spatio-Temporal Variation of Atmospheric Nutrient Deposition in Different Land Uses/Covers around Lake Kivu

Atmospheric deposition of nutrients, particularly nitrogen and phosphorus has the capacity to significantly affect the productivity and biogeochemistry of aquatic ecosystems. The objective of this study was to assess the impact of land use/cover types on the atmospheric deposition of nutrients around Lake Kivu. Dry and wet atmospheric deposition samples were collected from four different land use/cover types (forest, wetland, agricultural and urbanized area) at four stations (Goma, Lwiro, Bukavu and Iko) around the Lake Kivu basin. The highest annual loading of dry total phosphorus (TP) was recorded at a station located in an urban area at Goma (4.4 ± 3.9 μmol/m2/yr) and the highest dry deposition of total nitrogen (TN) was recorded at Iko (84.5 ± 41.2 μmol/m2/yr). High wet TP and TN were at Bukavu (0.7 ± 1.1 μmol/m2/yr) and Iko (21.7 ± 34.7 μmol/m2/yr) respectively. High dry TP loads were recorded in the forest area of Goma and the highest dry TN at Lwiro. High wet TP loads were record in agriculture at Goma and high values of wet TN in agriculture at Iko. Phosphorus and nitrogen deposition rates around Lake Kivu were similar to those reported for other African lakes. The highest rate of TP was recorded mainly in the forest area for dry deposition while high TN was recorded in all types of land use/cover in the basin. This study found out that forest traps high concentration of nutrient than other land uses/covers.