Nitrogen and Phosphorus Uptake Dynamics in Tropical Cerrado Woodland Streams

Nícolas Reinaldo Finkler,Flavia Tromboni,Davi Gasparini Fernandes Cunha,Iola Boëchat,Björn Gücker

doi:10.3390/w10081080

Nícolas Reinaldo Finkler, Flavia Tromboni + Show 3 more

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https://doi.org/10.3390/w10081080

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Abstract

Pollution abatement through phosphorus and nitrogen retention is a key ecosystem service provided by streams. Human activities have been changing in-stream nutrient concentrations, thereby altering lotic ecosystem functioning, especially in developing countries. We estimated nutrient uptake metrics (ambient uptake length, areal uptake rate, and uptake velocity) for nitrate (NO3–N), ammonium (NH4–N), and soluble reactive phosphorus (SRP) in four tropical Cerrado headwater streams during 2017, through whole-stream nutrient addition experiments. According to multiple regression models, ambient SRP concentration was an important explanatory variable of nutrient uptake. Further, best models included ambient NO3–N and water velocity (for NO3–N uptake metrics), dissolved oxygen (DO) and canopy cover (for NH4–N); and DO, discharge, water velocity, and temperature (for SRP). The best kinetic models describing nutrient uptake were efficiency-loss (R2 from 0.47–0.88) and first-order models (R2 from 0.60–0.85). NO3–N, NH4–N, and SRP uptake in these streams seemed coupled as a result of complex interactions of biotic P limitation, abiotic P cycling processes, and the preferential uptake of NH4–N among N-forms. Global change effects on these tropical streams, such as temperature increase and nutrient enrichment due to urban and agricultural expansion, may have adverse and partially unpredictable impacts on whole-stream nutrient processing.

Highlights

Streams are biogeochemical active systems that alter the amount and chemical form of nutrients and organic matter transported from their catchments to downstream systems [1,2]
We studied whole-stream NO3 –N, NH4 –N, and soluble reactive phosphorus (SRP) uptake across a gradient of ambient stream nutrient concentrations to expand our knowledge about interactions between N and P cycling and how these interactions are affected by nutrient availability in tropical streams
We studied four streams located in the Brazilian Cerrado savanna biome to address the following research questions: (1) How does nutrient uptake vary across a gradient of ambient nutrient availability? (2) How do the absolute and relative availability of one nutrient influence the uptake of the other nutrient? (3) Are there positive or negative relationships between NO3 –N, NH4 –N, and SRP uptake rates? (4) Are nutrient uptake rates higher or lower than those reported for temperate streams in the literature? In general, we hypothesized a higher demand for NH4 –N than for SRP and

Summary

Introduction

Streams are biogeochemical active systems that alter the amount and chemical form of nutrients and organic matter transported from their catchments to downstream systems [1,2]. Stream nitrogen (N) and phosphorus (P) retention is considered an important ecosystem service as it controls the export of these nutrients to downstream rivers, lakes, estuaries, and oceans, mitigating the negative consequences of cultural eutrophication [3,4]. Human activities have considerably altered nutrient availability, mobility, and distribution in freshwater systems [5,6,7], affecting ecosystem-wide nutrient and organic matter dynamics [8], and freshwater ecosystem functioning. Some empirical studies have considered multi-elemental effects and dynamics [24,25], but they are rare in tropical regions (but see [19]). Some authors have explored correlations between N and P uptake in streams including measurements of either nitrate–nitrogen (NO3 –N) [26,27] or ammonium–nitrogen (NH4 –N) [28,29], but rarely both

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