The impact of accelerating land-use change on the N-Cycle of tropical aquatic ecosystems: Current conditions and projected changes

Downing, John A.; McClain, Michael E.; Twilley, Robert R.; Mélack, John M.; Elser, James J.; Rabalais, Nancy N.; Lewis, William M.; Turner, R. Eugene; Corredor, Jorge E.; Soto, Doris; Yáñez‐Arancibia, Alejandro; Kopaska, Jeff; Howarth, Robert W.

doi:10.1007/978-94-011-4645-6_6

Cited by 78 publications

(113 citation statements)

References 97 publications

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“…Ecosystem alteration due to anthropogenic nutrient loading of coastal zones is occurring at a rapid rate in the tropics (Downing et al 1999). The impact on the ecological functioning of coastal ecosystems varies in intensity and spatial distribution, both locally and globally.…”

Section: Implications For Tropical Estuariesmentioning

confidence: 99%

“…The impact is expected to be greater in the tropics than at higher latitudes (Downing et al 1999) and on a global scale, tropical regions such as southeast Asia are particularly vulnerable in terms of ecosystem alteration due to anthropogenic nutrient loading (Mackenzie et al 2002;Jennerjahn et al 2004;Halpern et al 2008). The effects of altered nutrient cycling in tropical ecosystems can be understood most easily in the context of nutrient dynamics in undisturbed or minimally disturbed tropical ecosystems, however, nutrient processing in tropical estuaries, in general, is poorly studied relative to temperate environments (Downing et al 1999;Bianchi 2007) and there are even fewer studies comparing biogeochemical cycles in disturbed and undisturbed tropical systems Kristensen et al 2008). Additionally, these studies are often limited in the suite of processes measured, with much of the information available tending to be focused on individual processes (Boynton et al 2008).…”

Section: Introductionmentioning

confidence: 97%

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Effect of nutrient loading on biogeochemical processes in tropical tidal creeks

et al. 2011

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The effect of increased nutrient loads on biogeochemical processes in macrotidal, mangrovelined creeks was studied in tropical Darwin Harbour, Australia. This study uses an integrative approach involving multiple benthic and pelagic processes as measures of ecosystem function, and provides a comparison of these processes in three tidal creeks receiving different loads of treated sewage effluent. There were significant differences in process rates between Buffalo Creek (BC) (hypereutrophic), which receives the largest sewage loads; Myrmidon Creek (MC) (oligotrophic-mesotrophic) which receives smaller sewage inputs; and Reference Creek (RC) (oligotrophic) which is comparatively pristine.Benthic nutrient fluxes and denitrification were more than an order of magnitude higher and lower, respectively, in BC and denitrification efficiency (DE) was \10%. Pelagic primary production rates were also much higher in BC but respiration exceeded primary production resulting in severe drawdown of O 2 concentrations at night. Hypoxic conditions released oxide-bound phosphorus and inhibited coupled nitrification-denitrification, enhancing benthic nitrogen and phosphorus fluxes, leading to a build-up of excess nutrients in the water column. Poor water quality in BC was exacerbated by limited tidal flushing imposed by a narrow meandering channel and sandbar across the mouth. In contrast to BC, the effect of the sewage load in MC was confined to the water column, and the impact was temporary and highly localized. This is attributed to the effective flushing of the sewage plume with each tidal cycle. Denitrification rates in MC and RC were high (up to 6.83 mmol N m -2 day -1 ) and DE was approximately 90%. This study has identified denitrification, benthic nutrient fluxes and pelagic primary production as the biogeochemical processes most affected by nutrient loading in these tidal creek systems. Physical process play a key role and the combined influence of nutrient loading and poor tidal flushing can have serious consequences for ecosystem functioning.

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Section: Implications For Tropical Estuariesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 97%

Effect of nutrient loading on biogeochemical processes in tropical tidal creeks

et al. 2011

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“…Because of its high water volume, the Amazon River is the single largest source of nitrogen to the Brazilian coast, transferring approximately 3 Tg N yr )1 from land to ocean annually (Table 3), with 0.96 Tg N yr )1 in dissolved inorganic form. The Amazon basin is still considered pristine, but increasing deforestation and agriculture expansion in the region are likely to cause major impacts on the N-cycle and maybe increase nitrogen transport into aquatic systems (Downing et al 1999). The Tocantins River watershed is another important drainage system in the Amazon region, with a drainage area of 767,000 km 2 and annual mean discharge of 11,000 m 3 s )1 (Costa et al 2003).…”

Section: Export Of N In Wood and Other Productsmentioning

confidence: 99%

“…After the typical conversion of Amazon forests into pastures, rates of mineralization and nitrification tend to decrease, and reduce the nitrogen availability in soils and delivery rates to water bodies (Neill et al 1997;Melillo et al 2001). However, as natural vegetation and aging pastures are increasingly converted to intensive production of export crops such as soybeans, cotton and other lucrative crops, growing rates of both nitrogenous fertilizer consumption and biological nitrogen fixation in agriculture (Boddey et al 1997) are leading to increased inputs of anthropogenic Nr to the landscape and, eventually, to higher export of nitrogen to surface waters (Downing et al 1999).…”

Section: Introductionmentioning

confidence: 99%

Human activities changing the nitrogen cycle in Brazil

et al. 2006

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The production of reactive nitrogen worldwide has more than doubled in the last century because of human activities and population growth. Advances in our understanding of the nitrogen cycle and the impacts of anthropogenic activities on regional to global scales is largely hindered by the paucity of information about nitrogen inputs from human activities in fast-developing regions of the world such as the tropics. In this paper, we estimate nitrogen inputs and outputs in Brazil, which is the world's largest tropical country. We determined that the N cycle is increasingly controlled by human activities rather than natural processes. Nitrogen inputs to Brazil from human activities practically doubled from 1995 to 2002, mostly because of nitrogen production through biological fixation in agricultural systems. This is in contrast to industrialized countries of the temperate zone, where fertilizer application and atmospheric deposition are the main sources of anthropogenic nitrogen. In Brazil, the production of soybean crops over an area of less than 20 million ha, was responsible for about 3.2 Tg N or close to one-third of the N inputs from anthropogenic sources in 2002. Moreover, cattle pastures account for almost 70% of the estimated 280 · 10 6 ha of agricultural land in Brazil and potentially fix significant amounts of N when well managed, further increasing the importance of biological nitrogen fixation in the nitrogen budget. Much of these anthropogenic inputs occur in the Brazilian savannah region (Cerrado), while more urbanized regions such as the state of Sa˜o Paulo also have high rates of nitrogenous fertilizer inputs. In the Amazon, rates of anthropogenic nitrogen inputs are relatively low, but continuing conversion of natural forests into cattle pasture or secondary forests potentially add a significant amount of new nitrogen to Brazil given the vast area of the region. Better measurements of biological fixation rates in Brazil are necessary for improving the nitrogen budgets, especially at a more refined spatial scale.

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“…The most substantial human-induced perturbation of the N-cycle is attributed to agricultural activities, with exponentially increasing production and application of fertilizer (Schlesinger 1992;Gundersen et al 1994;Vitousek et al 1997;Downing et al 1999;Galloway et al 1995).…”

Section: Introductionmentioning

confidence: 99%

Nitrogen budget and gaseous nitrogen loss in a tropical agricultural watershed

2007

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Although agricultural systems in tropical monsoon Asia play a central role in the global nitrogen (N) cycle, details of the N cycle in this region on a watershed scale remain unclear. This study quantified the N budget in a tropical watershed of 221 km 2 on Java Island, where paddy fields cover 28% of the land, by conducting field surveys. The amount of net biochemical gaseous N loss to the atmosphere (X GB ), which is generally difficult to determine, was calculated as the residual of the N balance. Assuming that NH 3 volatilization balances deposition, and hence subtracting NH 4 -N from the N import with atmospheric deposition, the average total import and export of N per year was found to be 46.5 kg ha -1 year -1 over the watershed. Of this, 71% was imported as fertilizer (M F ) and 29% with atmospheric deposition (M AD ). On the export side, 42% was lost as X GB , 37% with incineration of rice residues and wood fuel (X GI ), 13% with river discharge (X D ) and 9% with rice surplus export (X R ). A large portion of X GB , and consequently, a small portion of X D could be explained by the high rate of denitrification resulting from the high temperature and humid climate, and are thought to be common features of tropical watersheds where paddy fields are found.

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The impact of accelerating land-use change on the N-Cycle of tropical aquatic ecosystems: Current conditions and projected changes

Cited by 78 publications

References 97 publications

Effect of nutrient loading on biogeochemical processes in tropical tidal creeks

Effect of nutrient loading on biogeochemical processes in tropical tidal creeks

Human activities changing the nitrogen cycle in Brazil

Nitrogen budget and gaseous nitrogen loss in a tropical agricultural watershed

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