Dissolved nutrient exports from natural and human‐impacted N eotropical catchments

Abstract

Aim Neotropical biomes are highly threatened by land‐use changes, but the catchment‐wide biogeochemical effects are poorly understood. Here, we aim to compare exports of dissolved nitrogen ( N ) and phosphorus ( P ) from natural and human‐impacted catchments in the N eotropics. Location N eotropics. Methods We measured streamwater nutrient concentrations and exports in 20 south‐eastern B razilian catchments with different land uses (natural C errado/semi‐deciduous forest, pasture, intensive agriculture and urban areas) and conducted a meta‐analysis on nutrient exports from N eotropical catchments, both natural and human‐impacted. Results Organic forms dominated dissolved nutrient exports in central/south‐east B razil in both natural and human‐dominated catchments. Our meta‐analysis suggests that there is wide geographic variability in the natural dominance of organic versus inorganic nutrient exports across the N eotropics, and for N a tendency for inorganic and organic forms to vary inversely across sites. We found strong land‐use effects, especially in urban areas. In areas naturally dominated by organic N exports, land use did not overturn that dominance, but rather increased the concentration of both inorganic and organic N . In catchments dominated by inorganic N exports or showing equivalent organic and inorganic exports, land use also caused organic exports to be dominant. Land‐use effects on P were unclear, probably owing to a paucity of available data, but our results from south‐east B razil suggested that land use also increases dissolved P exports. Main conclusions We show that dominance of inorganic versus organic nutrient exports is highly variable across natural Neotropical catchments, a pattern contrasting with the general tendency for dominance of organic N in natural temperate catchments. Further, we found a general dominance of organic N in most human‐impacted catchments, which is in contrast to strong dominance of inorganic N in most human‐impacted temperate catchments. Finally, we find that urbanization exerts the strongest impacts on nutrient exports, thus underscoring wastewater treatment as a critical management priority under future land‐use change.

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