Multiproxy paleolimnological reconstruction of Lake Victoria’s environmental history, East Africa

<p>Lake Victoria (LV), Africa’s largest lake is situated in the African Great Rift Valley. Due to its shallowness (max.68 m; mean 40 m) and limited river inflow, LV is very sensitive to variations in climate and lake level fluctuations. As a result, LV has undergone repeated low stand periods, or even complete desiccation during the Late Pleistocene with profound effects on the aquatic ecosystem. One example is the emergence of a unique biodiversity of endemic cichlid species following the lake’s last desiccation event during the last glacial and subsequent refilling commencing ~15,000 years ago.</p><p>In an interdisciplinary project we aim at reconstructing linkages between paleoenvironmental variability, disturbances and adaptive species radiation by combining approaches from paleogenomics, paleoecology and paleolimnology. For this purpose, four sediment cores along a depth-transect (near-shore to offshore), covering ca. the past 14,000 years, are analyzed.</p><p>We present first paleolimnological results of long-term changes of using (isotope-)geochemical indicators including: Sedimentary pigments and biogenic silica to infer aquatic productivity supported by micro X-ray Fluorescence (XRF) derived element geochemistry, <sup>13</sup>C and <sup>15</sup>N, and sedimentary phosphorus fraction analyses providing information on changes in sediment composition.</p><p>The results suggest that the infilling of the LV basin was a long-term step-wise process. This is shown by elevated and variable indicators for lithogenic input (e.g Ti, Zr and K) and interpreted as mobilization of substrate from the shorelines by a dynamic lake level prior to its stabilization in the Early and Mid-Holocene.  This process is mainly reflected in the core taken at the greatest water depth (65 m). Simultaneously, the aquatic productivity (BSi and chloropigments) increased rapidly after the refilling of the lake basin in the Late-Glacial. A gradual drying of the climate and a following shift to a more oxygenated water column is observed in the Mid-to Late Holocene indicated by a decline in chemically weathered material (e.g Rb/K & K/Al ratios) and abundance of Mn.</p>

Characterizing variations of dissolved organic matter (DOM) properties in Nansi Lake: an important reservoir along the eastern route of China’s South-to-North Water Diversion Project

Variations in dissolved organic matter (DOM) quality has far-reaching implications that affect, e.g., aquatic productivity, food web structures, trace element and pollutant transport. In this study, a total of 186 water samples were collected at 62 sites (three points in time within one year) in Nansi Lake. UV-Vis spectra, Synchronous fluorescence (SF) spectra, the excitation-emission matrix and parallel factor analysis (EEM-PARAFAC) were applied to indicate the source and quality of DOM. Water transferring of the eastern route of China’s South-to-North Water Diversion Project had a great influence on the water level of Nansi Lake. Results of SF spectra, EEM-PARAFAC and principal component analysis (PCA) suggested that protein-like substances played a more important role in DOM properties in April and July than October. This result is related to a high fluorescence intensity occurred in April (Fmax=0.72±0.03 in the upper lake and 1.84±0.13 in the lower lake) and July (Fmax=1.10±0.05 in the upper lake and 1.49±0.04 in the lower lake), which might be caused by water transferring from other lakes to Nansi Lake, death and decomposition of submerged plants. At the same time, relatively good correlations were found between humic-like substances, DOC and a254 in April, July and October, which indicated the important contribution of humic-like substances to Nansi Lake. With the completion of the water diversion, the ratio of the fluorescence intensity of component to the total fluorescence intensity (%Fmax) suggested that the proportion of humic-like substances started to increase. And when it came to October, humic-like substances become the main substance in DOM collected from Nansi Lake (%Fmax=66.56%±0.58% in the upper lake and 61.98%±0.99% in the lower lake). Moreover, among the two areas in Nansi Lake, the upper lake always had a higher degree of humification (HIX=2.23±0.06, 2.38±0.11 and 3.10±0.05 in April, July and October, respectively) than the lower lake (HIX=1.06±0.05, 1.68±0.05 and 2.62±0.08 in April, July and October, respectively), which implied extraneous contaminants might have a more important impact on DOM properties in the upper lake.

Biomass of Eichhornia crassipes, (Mart) Solms. In the Chacororé–Sinhá Mariana, lake System Pantanal of Mato Grosso, Brazil

The Pantanal constitutes the biggest floodplain of the world, forming a mosaic of different habitats, sustaining rich aquatic and terrestrial biota. This mosaic of habitats of the Pantanal is well represented in the Barão de Melgaço region by the Chacororé-Sinhá Mariana Lake System, this system of parental lakes of Cuiabá river are recognized by their aquatic productivity and scenically beauty. The aquatic macrophyte are very abundant organisms being considered the most productive community in the aquatic system, with great capacity of accumulate biomass and nutrients. The samples were collected into three stations representing the Chacororé-Sinhá Mariana lakes and the transition between them. This study had as purpose to evaluate the spatial and temporal dynamic of biomass in E. crassipes in the stands of this specie in Chacororé-Sinhá Mariana “baía” system. The results shown that both lakes shown bigger biomass during flood, and that in transition sample area were verified the bigger biomass of studied areas. This research supports another studies realized in the Pantanal about the importance of the “flood pulse” in the temporal variation of the biomass and shown that the variation of the biomass of E. crassipes in the lakes evidence the spatial heterogeneity which exists between those lakes. In this way the aquatic macrophyte can indicate the impacts resulting of the hydrological changes in this system of lakes.

ANALYSIS OF YELLOWFIN TUNA (Thunnus albacares) FISHING GROUND BASED ON SEA SURFACE TEMPERATURE AND CHLOROPHYLL-A IN THE WEST SUMATERA WATERS

This research was conducted on September 2019 in west Sumatera waters which was aimed to find out the level of aquatic productivity, to analyze the yellowfin tuna fishing ground and to find out the corelation between sea surface temperature (SST) and chlorophyll-a with the total catch of yellowfin tuna. In conducting the research, survey and spatial analyze were used as the method. The highest total catch of yellowfin tuna was on October 2019 with the total 60.610 kg and the CPUE 166 kg/trip. On the other hand, the lowest total catch was on June with the total 18.080 kg and CPUE 92,7179 kg/trip. Based on the result of the CPUE, October is the best month for fishing. The correlation coefficient between SST and total catch in 2018 was -0.69 which mean there was a negative correlation. Meanwhile, the correlation chlorophyll-a with the total catch was 0.65 which mean the corelation between both variables were not good

Understanding potential drivers of aquatic metabolism in a subtropical treatment wetland

Changes of dissolved oxygen (DO) in aquatic ecosystems integrates dynamic biological, physical and chemical processes that control the rate of ecosystem metabolism. Aquatic ecosystem metabolism can be characterized by the diel change in DO changes over time and is expressed as the net aquatic productivity (NAP). This study investigated aquatic metabolism of dominant emergent and submerged aquatic vegetation (EAV and SAV, respectively) within two treatment flow-ways (FW) of Stormwater Treatment Area 2 (STA-2) in the Everglades ecosystem. The hypothesis of this study is that aquatic metabolism will differ between aquatic vegetation communities with SAV communities will have a greater GPP and ER rate than EAV communities driven by biophysical, hydrodynamic and biogeochemical differences between systems. Aquatic metabolism observed in this study vary spatially (along FWs) and temporally (diel to days) controlled by different effects related biological, physical and chemical processes. This study suggests that ecosystem metabolism is controlled differently across FWs with varying levels of response to loading/transport and water column attributes resulting in differences in organic matter accumulation, C turnover and phosphorus cycling.

Spatiotemporal variations of organic matter sources in two mangrove-fringed estuaries in Hainan, China

<p>Mangrove systems represent important long-term sinks for carbon since they have much higher carbon burial rates than terrestrial forests or typical coastal ecosystem. However, quantifying the sources of organic matter (OM) in estuarine and coastal sediments, where mangroves occur but are not the only source of OM, is challenging due to the variety of OM sources and diverse transport processes in these dynamic environments. The sources of OM in surface sediments of two mangrove-fringed estuaries in Hainan Province, China, were investigated using the mangrove specific biomarker taraxerol and other lipid biomarkers, as well as stable carbon isotopes. Mixing models based on the concentration of taraxerol, plant wax <em>n</em>-alkanes and δ<sup>13</sup> C<sub>OM</sub> indicate that terrestrial non-mangrove plant OM accounted for 52-72% of the OM in the two estuaries, aquatic OM from phytoplankton and/or seagrass accounted for 8-29%, and OM from mangroves comprised 16-26% of the total. Terrestrial plants contributed 16-20% more of the OM to sediments of Bamen Bay, which is on the wetter, eastern side of Hainan Island, than to Danzhou Bay, but aquatic OM (algae plus seagrass) fraction was 17% lower than that in Danzhou Bay sediments. In both estuaries, mangrove and aquatic OM fractions increased seaward while the terrestrial OM fraction decreased. Terrestrial fraction in BMB sediments is 12% higher in summer compared to autumn, which is offset by a comparable reduction in the mangrove OM fraction, as well as higher aquatic OM fractions in both estuaries. This may be caused by enhanced river discharge, more efficient mangrove leaf litter transport offshore, and/or higher aquatic productivity. The biomarker and carbon isotope approach used here can be applied to semi-quantitatively estimate spatial and temporal variations of the sources of organic carbon in tropical estuarine and coastal sediments, a major sink for carbon in the ocean.</p>

The browning and re-browning of lakes: Divergent lake-water organic carbon trends linked to acid deposition and climate change

Dissolved organic carbon (DOC) concentrations and water colour are increasing in many inland waters across northern Europe and northeastern North America. This inland-water “browning” has profound physical, chemical and biological repercussions for aquatic ecosystems affecting water quality, biological community structures and aquatic productivity. Potential drivers of this “browning” trend are complex and include reductions in atmospheric acid deposition, changes in land use/cover, increased nitrogen deposition and climate change. However, because of the overlapping impacts of these stressors, their relative contributions to DOC dynamics remain unclear, and without appropriate long-term monitoring data, it has not been possible to determine whether the ongoing “browning” is unprecedented or simply a “re-browning” to pre-industrial DOC levels. Here, we demonstrate the long-term impacts of acid deposition and climate change on lake-water DOC concentrations in low and high acid-deposition areas using infrared spectroscopic techniques on ~200-year-long lake-sediment records from central Canada. We show that acid deposition suppressed naturally higher DOC concentrations during the 20th century, but that a “re-browning” of lakes is now occurring with emissions reductions in formerly high deposition areas. In contrast, in low deposition areas, climate change is forcing lakes towards new ecological states, as lake-water DOC concentrations now often exceed pre-industrial levels.

Temporal Variations of Water Quality Parameters, Phytoplankton, And Invertebrates In Environmental Change Hotspots: A Case of Lake Wamala, Uganda

Lake Wamala (Uganda) is a small shallow lake (maximum mean depth = 4.5m) that has periodically undergonefluctuations in depth and area because of changes in rainfall, temperature and wind speed. No study, however,has been done to assess how these changes, in addition to catchment degradation, which are likely to intensify in future, have affected aquatic productivity processes. Data on Secchi depth (SD), turbidity, conductivity, dissolved oxygen (DO), total phosphorous (TP), soluble reactive phosphorus (SRP), soluble reactive silicon (SRSi), ammonia (NH4-N), nitrite nitrogen (NO2-N), nitrate nitrogen (NO3-N), Chlorophyl a, composition and abundance of algae, and invertebrates were compared between periods 1998-2000 and 2011-2013. Results showed a twofold increase in conductivity and TP, a threefold increase in SRSi, chlorophyll a > 25 ?g l-1, and persistence by low water transparency (SD < 0.7 m). In consequence, algal biomass increased by >70%, with emergence of new species, especially among the dinoflagellate and euglenophyte groups. Although rotifers, which are known to have capacity to withstand stressful habitat conditions, dominated the zooplankton, their density decreased by >80%. The phantom-midge, chaoborus, and the midge, chironomid, larvae dominated macro-invertebrate, but did not show clear trends between the two periods.