Comparative analysis of rating curve and ADP estimates of instantaneous water discharge through estuaries in two contrasting Brazilian rivers

Abstract

Abstract:This work quantifies, using ADP and rating curve techniques, the instantaneous outflows at estuarine interfaces: higher to middle estuary and middle to lower estuary, in two medium-sized watersheds (72 000 and 66 000 km 2 of area, respectively), the Jaguaribe and Contas Rivers located in the northeastern (semi-arid) and eastern (tropical humid) Brazilian coasts, respectively. Results from ADP showed that the net water balances show the Contas River as a net water exporter, whereas the Jaguaribe River Estuary is a net water importer. At the Jaguaribe Estuary, water retention during flood tide contributes to 58% of the total volume transferred during the ebb tide from the middle to lower estuary. However, 42% of the total water volume (452 m 3 s 1 ) that entered during flood tide is retained in the middle estuary. In the Contas River, 90% of the total water is retained during the flood tide contributing to the volume transported in the ebb tide from the middle to the lower estuary. Outflows obtained with the rating curve method for the Contas and Jaguaribe Rivers were uniform through time due to river flow normalization by dams in both basins. Estimated outflows with this method are about 65% (Contas) and 95% (Jaguaribe) lower compared to outflows obtained with ADP. This suggests that the outflows obtained with the rating curve method underestimate the net water balance in both systems, particularly in the Jaguaribe River under a semi-arid climate. This underestimation is somewhat decreased due to wetter conditions in the Contas River basin.

Chronological Trends and Mercury Bioaccumulation in an Aquatic Semiarid Ecosystem under a Global Climate Change Scenario in the Northeastern Coast of Brazil

“…The results regarding Hg in surface sediments and SPM are indicative of the increase in ocean forcing due to heat accumulation over the continental shelf and further, into the estuary, that promotes a greater entry of the saline wedge into the estuarine zone [87]. Similar to what was observed in previous works, these processes strongly affect the hydrodynamics of these aquatic environments [87][88][89][90], inducing maximum turbidity zone retreat and favoring the incorporation of fine sediments into the seawater column [88,92]. Climate change could be the most important reason for the intensification of these processes and is a very possible scenario in a mangrove area such as the Ceará River estuary, that would be further invaded by seawater, resulting in a greater mobilization of bioavailable Hg, even due to a greater complexation with chlorides (advancing further upstream), which does allow an acceleration of the biogeochemical transformation of Hg [56].…”

“…In the northeastern regions of Brazil, the regional and global drivers responsible for increasing continental runoff and diminishing fluvial discharges to the Western Equatorial South Atlantic Ocean are strengthening due to global warming [56,[87][88][89][90]. This region is normally already subject to conditions of semiarid characteristics, but drought events are now intensifying both in terms of their frequency and in the duration of prolonged drought episodes [50,91].…”

Obliquity Influence on Low‐Latitude Coastal Precipitation in Eastern Brazil During the Past ∼850 kyr

“…This is due to the association of K with minerals that are characteristic of dry regions with low rates of chemical weathering (e.g., potassium feldspar, illite; Calvert, 1976; Yarincik et al., 2000; Zabel et al., 2001) and the association of Al with fine‐grained clay minerals derived from intense chemical weathering (Calvert, 1976). In Core M125‐73‐3, we interpret ln (K/Al) ratios to represent changes in chemical weathering intensity in the coastal lowlands (Figure 4e), which are the wettest portion of the Contas catchment and thus the main source of riverine run‐off (Da Silva Dias et al., 2011). Since the rate of chemical weathering is directly dependent on continental moisture availability, we posit that the ln (K/Al) proxy indirectly records past hydroclimate changes in the coastal zone of the Contas basin.…”

“…The core location is ∼51 km away from the mouth of the Contas River, which is the main source of terrigenous sediments to the core site (Text S1 and Figure S2 in Supporting Information S1) The main channel of the river crosses several climatically distinct regions, including the semi-arid mountainous hinterland, the semi-humid lower middle course and the very humid coastal zone (Figure 1b). Thus, precipitation within the catchment is highly variable, with the wettest section being the lower basin near the coast, which is responsible for >50% of the net riverine discharge (Da Silva Dias et al, 2011). Since runoff from the Contas catchment is largely derived from rainfall in the coastal lowlands, Core M125-73-3 is dominantly influenced by coastal rather than hinterland precipitation changes.…”

Estimación del caudal a partir de la evolución del nivel del agua en un estuario con onda de marea estacionaria

“…Para numerosos ríos a lo largo del mundo, Petersen-Overlier et al [22] observaron que el método de la regla limnimétrica presenta gran incertidumbre para caudales medianos y pequeños, y muy baja ante el movimiento de grandes volúmenes de agua. Da Silva Dias et al [23] compararon los resultados obtenidos de mediciones de flujos de salida de dos cuencas hidrográficas medianas, las de los ríos Jaguaribe y Contas (72.000 y 66.000 km 2 , respectivamente) localizadas sobre las costas noreste (semiárida) y oriental (húmeda tropical), respectivamente, de Brasil. Ellos aplicaron las técnicas convencionales de la curva velocidad-nivel del agua y la perfilometría acústica (ADP) para definir el método más apropiado según las características transicionales entre los sectores estuarinos superior a medio y medio a inferior.…”