Influence of seasonal flooding on soil total nitrogen, organic phosphorus and microbial populations in the Okavango Delta, Botswana

Mubyana, T.; Krah, Martin; Totolo, Otlogetswe; Bonyongo, Mpaphi C.

doi:10.1006/jare.2002.1095

Cited by 21 publications

(19 citation statements)

References 17 publications

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“…After boosting the amount of total-P at the beginning of the flooding season, phosphorus continuously declines, as no other source supplements the loss towards the end of the season. It also implies that the phosphorus availability from dry organic matter is very limited, supporting earlier findings of low P-content in floodplain soils deeper than 0,1 m (Mubyana et al 2003). However, island soils still show much higher concentrations of P than floodplain soils Mubyana et al 2003) and groundwater underneath islands on or adjacent to floodplains generally accumulates ion species, which are transferred there from the floodplain by biological activity (McCarthy et al 1993).…”

Section: Nutrient Status Of the Seasonal Floodplainmentioning

confidence: 56%

“…Nutrient availability of soils in the Okavango Delta is limited to the soil surface, where considerable amounts of nutrients have been found . Processes and budgets for water-soluble ions, especially for the short time span of 2-3 weeks at the onset of floods, and their relation to the hydrograph in seasonal floodplains are of crucial importance (Mubyana et al 2003;Koschorrek and Darwich 2003). This is because the availability of soluble nutrients triggers numerous biological processes, especially the boost of primary production rates of floodplains (Bonyongo 1999) and hatching of phyto-and zooplankton (Hogberg et al 2002).…”

Section: Introductionmentioning

confidence: 98%

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Nutrient Budget in the Seasonal Wetland of the Okavango Delta, Botswana

Krah

McCarthy

Huntsman-Mapila

et al. 2006

Wetlands Ecol Manage

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The nutrient (P and N species) and chloride budgets were investigated in a representative floodplain in the seasonal wetlands of the Okavango Delta, Botswana. A variety of sources of nutrients in the surface water were considered, namely ion species coming with the floodwater, those generated from dry floodplain soils and those from water-soluble dust deposition (both local and long-range sources). Concentrations of total-nitrogen and chloride in surface water were below 1 mg l À1 . Total-phosphorus concentrations were 0.05 mg l À1 , reflecting the oligotrophic character of the system. Dust deposition rates were highest for chloride at 2.44 g m À2 year À1 followed by 0.79 g m À2 year À1 for total-N, 0.40 g m À2 year À1 for ammonia and only 0.02 g m À2 year À1 for total-P, respectively. Chloride was derived primarily from long-range transport, while N and P species were of more local origin. Dissolution rates for these ions combined were calculated to be 3.9 g m À2 for the flooded area in the 1999 season and thus all dry deposits must be re-dissolved. The accumulation of dust deposits on dry surfaces and their subsequent dissolution causes 2-5 times higher concentrations of nitrogen, phosphorus and chloride with the onset of the flood, thus boosting the nutrient stock in the crucial phase of the onset of flooding. Chloride dissolved from dry soil surfaces and dust contributed approximately 40% to the overall floodplain budget. Although contributions from the soil surface and dust to the nitrogen and phosphorus pools of the floodplain are less prominent (with 10% of total), they nonetheless represent a significant source of nutrients in the entire system. Extrapolation to annually flooded swamps (10,000 km 2 ) indicates a maximum contribution of 40% for total-nitrogen and 60% for total-phosphorus from dust deposition on wet or dry surfaces to the nutrient pool of the water body.

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Section: Nutrient Status Of the Seasonal Floodplainmentioning

confidence: 56%

Section: Introductionmentioning

confidence: 98%

Nutrient Budget in the Seasonal Wetland of the Okavango Delta, Botswana

Krah

McCarthy

Huntsman-Mapila

et al. 2006

Wetlands Ecol Manage

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“…Dung from mammals prior to flooding appears as the only probable source for this local eutrophication. Mubyana et al (2003) compared the phosphorus content in the soil on the same floodplain, before and after arrival of the flood. They found significant nutrient enrichments close to the soil surface, but recorded a significant nutrient depletion after arrival of the flood, suggesting that the water was nutritionally subsidized from the soil.…”

Section: Discussionmentioning

confidence: 99%

Zooplankton succession on seasonal floodplains: surfing on a wave of food

Lindholm

Hessen

2007

Hydrobiologia

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Floodplains represent ecotones with frequent high productivity mediated by regular shifts between aquatic and terrestrial ecosystems. We examined interactions along this intercept on a seasonal floodplain of the Okavango Delta, Botswana. We focused on the zooplankton communities in order to gain knowledge on the energetic and stoichiometric interplay of the two systems involved. A conspicuous horizontal migration and pulsed biomass increase was found for the dominant zooplankton species (Moina micrura, Daphnia laevis, Mesocyclops leuckarti), culminating in truly extreme numbers before a final collapse. There was a distinct succession in the peak abundance of these species, apparently subsidized by hatchlings from the seed bank of resting eggs as the flood proceeded over the savannah. The high productivity of the system seems to be driven by a strong coupling of the terrestrial and aquatic phase of the floodplains via a mobilization of terrestrially derived nutrients, through nutrients from grazing ungulates during dry periods. Carbon of terrestrial origin, however, appeared to be of minor importance for the planktonic part of the food web.

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“…This was attributed to possible leaching in the sandy floodplain and island soils or denitrification in the Delta's woodland areas (Staring, 1978;Davidson and Leonardson, 1998). In the same study by Mubyana et al (2003), TP was reported to range from 0.02 to 0.52%. It was observed that flooding significantly increased levels of TP on the islands, most probably due to desorption of phosphorus from flooded soils and peat areas in the presence of excess water (Brady, 1990). )…”

Section: Total Nitrogen and Phosphorusmentioning

confidence: 78%

“…Phosphate usually precipitates from solution with calcium, iron and aluminium or is incorporated into organic matter. Nitrogen and phosphate are often the limiting factor in eutrophication of water bodies (Mubyana et al, 2003). The resultant increase in growth of algae may cut off the supply of oxygen and sunlight to other aquatic organisms and thus result in subsequent loss of biodiversity within the ecosystem.…”

Section: Introductionmentioning

confidence: 99%

Water quality in the Okavango Delta

Mmualefe¹,

Torto²

2011

WSA

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The Okavango Delta ecosystem sustains a large number of plant and animal species as well as providing resources for the livelihood of the riparian human population. Despite changes in flow patterns, rainfall and other climatic conditions over the past decades, the system has responded well to maintain low salt-water balances through evapotranspiration and chemical precipitation processes. The electrical conductivity and total dissolved solids are generally low, with values less than 200 µS•cm -1 and averaging 40 mg•ℓ -1, respectively. The dissolved oxygen and dissolved organic carbon range from 1.8 to 8.8 and 5 to 15 mg•ℓ -1 , respectively, while pH ranges from 6.7 to 10.3. Total nitrogen and phosphorus are generally low with maximum concentrations of 1.7 and 1.6 mg•ℓ -1 , respectively, recorded downstream of the Delta. Even though most of these quality parameters are within limits for potable water, the Delta's ecosystem needs to be protected from anthropogenic activities. Past use of persistent organic pollutants requires monitoring of impacts of their residues on the plants and animal species within the ecosystem, in order to maintain its rich biodiversity. This review focuses on chemical quality data for water and sediments in the Okavango Delta published between 2000 and 2010. Despite the shortage of published data, it is hoped that this review will provide an overall picture of the status quo of the Delta's water and will set the direction for future monitoring efforts.

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Influence of seasonal flooding on soil total nitrogen, organic phosphorus and microbial populations in the Okavango Delta, Botswana

Cited by 21 publications

References 17 publications

Nutrient Budget in the Seasonal Wetland of the Okavango Delta, Botswana

Nutrient Budget in the Seasonal Wetland of the Okavango Delta, Botswana

Zooplankton succession on seasonal floodplains: surfing on a wave of food

Water quality in the Okavango Delta

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