Relationship among physicochemical conditions, chlorophyll-a concentration, and water level in a tropical river–floodplain system

Abstract

The free-flowing Usumacinta River maintains an average annual water-level fluctuation of 6.7 m. This study evaluated relationships between 14 physicochemical and biological variables and key factors in four water-level conditions in a riverfloodplain system. The analysis incorporated intra-annual variation in all variables, with each selected in accordance with multiple statistical and physicochemical criteria. Possible correlations were examined as a function of various physicochemical and biological factors at each water level. Within the study area, defined by a temporal gradient in principal component 1, the yearly river overflow above the bankfull stage is characterized by water with a low level of total suspended solids. Data on riverine wetlands suggest that seasonal changes are key to determining intra-and inter-annual chlorophyll-a levels and water clarity. However, opposite trends are observed for high and low water-level conditions. Nutrient enrichment cannot be taken as the key physicochemical factor of water level, under either water-level conditions, due to the lack of a temporal gradient in principal component 2 and the high biochemical variability of nitrate and orthophosphate levels. In conclusion, the hypothesis was accepted for the production of phytoplankton biomass and light attenuation at low and high water levels, as both were dependent on intra-annual changes. The increases in chlorophyll-a related to the minimal variability at the lowest water level open the opportunity to gauge this relationship as a possible environmental predictor for river-floodplain systems.

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“…Likewise, the persistence in time of the hypereutrophic conditions (Chl-a and TP) in the Maluco river-floodplain system agree with other results in hydraulically altered river-floodplain systems (Pinilla, 2010;Reckendorfer et al, 2013;Li et al, 2019), or with different interannual times of hydraulic connection (McKinney & Charpentier, 2009). Instead, the variation of Chl-a and nutrients in non-perturbed river-floodplain systems differed significantly in relation to WL, mainly between low and high water level (Brito et al, 2014;Tubatsi et al, 2014;Roach et al, 2014;Cruz-Ramírez et al, 2019). Indeed, the maintenance of the water connectivity conditions, natural flow cycles, and flood pulses is indispensable to keep the biogeochemical processes that maintain the ecological functions and services provided by the river-floodplain systems (Junk & Wantzen, 2004;Marton et al, 2015).…”

“…In this way, the values of chlorophyll-a (Chl-a) and nutrients are influenced by the lateral exchange of water due to temporal flooding, residence times and inputs of organic matter by runoff (Tubatsi et al, 2014;Fritz et al, 2018). For example, the increase of algal biomass has been frequently recorded during the low water level (WL) condition (Brito et al, 2014;Roach et al, 2014;Cruz-Ramírez et al, 2019). On the contrary, its decrement has been recorded in conditions of high WL (for example, Noe et al, 2013) since its fluctuation has been linked to the flood pulse that allows the dispersion of the planktonic community in areas with seasonal inundation (Junk & Wantzen, 2004;Noe et al, 2013).…”

“…On the contrary, its decrement has been recorded in conditions of high WL (for example, Noe et al, 2013) since its fluctuation has been linked to the flood pulse that allows the dispersion of the planktonic community in areas with seasonal inundation (Junk & Wantzen, 2004;Noe et al, 2013). Moreover, the enrichment in nitrogen and phosphorus has been indistinctly mentioned as a dominant abiotic processes tied to the spatial-temporal variability in the WL of the river-floodplain systems (for example, Brito et al, 2014;Tubatsi et al, 2014;Cruz-Ramírez et al, 2019).…”

“…However, the high variability of the concentrations of nutrients in short times regarding the inter-annual fluctuation of the WL can enhance the eutrophication (carbon, nitrogen, phosphorus), which in turn increase the phytoplankton biomass (Dodds, 2007;Cruz-Ramírez et al, 2019). Additionally, wastewater discharges, diffuse input of agricultural nutrients, runoffs and hydraulic disconnection are other causes associated with the enhancement of nutrients in river-floodplain systems (Cetin 2009;Sharma et al, 2010;Sánchez et al, 2012;Jeppesen et al, 2015;Lázaro-Vázquez et al, 2018).…”

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“…However, the high variability of the concentrations of nutrients in short times regarding the inter-annual fluctuation of the WL can enhance the eutrophication (carbon, nitrogen, phosphorus), which in turn increase the phytoplankton biomass (Dodds, 2007;Cruz-Ramírez et al, 2019). Additionally, wastewater discharges, diffuse input of agricultural nutrients, runoffs and hydraulic disconnection are other causes associated with the enhancement of nutrients in river-floodplain systems (Cetin 2009;Sharma et al, 2010;Sánchez et al, 2012;Jeppesen et al, 2015;Lázaro-Vázquez et al, 2018).…”