Flamingos and drought as drivers of nutrients and microbial dynamics in a saline lake

Abstract

Waterbird aggregations and droughts affect nutrient and microbial dynamics in wetlands. We analysed the effects of high densities of flamingos on nutrients and microbial dynamics in a saline lake during a wet and a dry hydrological year, and explored the effects of guano on prokaryotic growth. Concentrations of dissolved organic carbon, total phosphorus and total nitrogen in the surface waters were 2–3 fold higher during the drought and were correlated with salinity. Flamingos stimulated prokaryotic heterotrophic production and triggered cascading effects on prokaryotic abundance, viruses and dissolved nitrogen. This stimulus of heterotrophic prokaryotes was associated with soluble phosphorus inputs from guano, and also from sediments. In the experiments, the specific growth rate and the carrying capacity were almost twice as high after guano addition than in the control treatments, and were coupled with soluble phosphorus assimilation. Flamingo guano was also rich in nitrogen. Dissolved N in lake water lagged behind the abundance of flamingos, but the causes of this lag are unclear. This study demonstrates that intense droughts could lead to increases in total nutrients in wetlands; however, microbial activity is likely constrained by the availability of soluble phosphorus, which appears to be more dependent on the abundance of waterbirds.

Quantifying nutrient inputs by gulls to a fluctuating lake, aided by movement ecology methods

“…Expressed in hectares, the average nutrient inputs by the gulls in FP amount to 10.17 kg N ha −1 year −1 and 2.07 kg P ha −1 year −1 (Figure S3). Total nutrient load by flamingos at FP was estimated as 16.7 kg N ha −1 year −1 and 1.24 kg P ha −1 year −1 , but these inputs are concentrated during the summer months when flamingos breed (Batanero et al., ). Atmospheric inputs were estimated as 5.89 kg N ha −1 year −1 and 0.18 kg P ha −1 year −1 for the study region (Morales‐Baquero, Pulido‐Villena, & Reche, ).…”

“…Batanero et al. () reported a TN:TP ratio of 49:1 (range 25–85) in the dry year 2011–2012 and 52:1 (range 30–93) in the wet year 2010–2011. Therefore, P appears to limit in the system based on the Redfield ratio 16:1 at which primary production is expected to switch from N‐limitation to P‐limitation (Redfield, ).…”

“…Furthermore, reductions in water level in dry years and due to human activities (Rodríguez‐Rodríguez et al., ) increase nutrient concentrations in the FP water column by three‐fold (Batanero et al., ). Ongoing climate change in Andalusia acts in synergy with nutrient loading and water extraction to further enhance their impacts (Espinar, Diaz‐Delgado, Bravo‐Utrera, & Vila, ), and reductions in nutrient loading are required to ensure that Mediterranean wetlands such as FP maintain their resilience to climate change (Green et al., ).…”

“…The biogeochemical effects of gull guano are probably strongly conditioned by the high salinity of the lake, which is likely to reduce methane production but increase phosphate release from the sediment (Camacho et al, 2017;Clavero, Fernandez, & Niell, 1990). The water column in FP holds higher concentrations of N than of P, but nutrient dynamics are highly dependent on hydrology (Batanero et al, 2017;García et al, 1997). Batanero et al (2017) reported a TN:TP ratio of 49:1 (range 25-85) in the dry year 2011-2012 and 52:1 (range 30-93) in the wet year 2010-2011.…”

“…The water column in FP holds higher concentrations of N than of P, but nutrient dynamics are highly dependent on hydrology (Batanero et al, 2017;García et al, 1997). Batanero et al (2017) reported a TN:TP ratio of 49:1 (range 25-85) in the dry year 2011-2012 and 52:1 (range 30-93) in the wet year 2010-2011. Therefore, P appears to limit in the system based on the Redfield ratio 16:1 at which primary production is expected to switch from N-limitation to P-limitation (Redfield, 1958).…”