An analysis of primary production in the Daly River, a relatively unimpacted tropical river in northern Australia

Abstract

In this paper, the dynamics of primary production in the Daly River in tropical Australia are investigated. We used the diurnal-curve method for both oxygen and pH to calculate photosynthesis and respiration rates as indicators of whole-river productivity. The Daly River has maximum discharges during the summer, monsoonal season. Flow during the dry season is maintained by groundwater discharge via springs. The study investigated how primary production and respiration evolve during the period of low flow in the river (April–November). The relationship between primary production and the availability of light and nutrients enabled the role of these factors to be assessed in a clear, oligotrophic tropical river. The measured rate of photosynthesis was broadly consistent with the estimated mass of chlorophyll associated with the main primary producers in the river (phytoplankton, epibenthic algae, macroalgae, macrophytes). A significant result of the analysis is that during the time that plant biomass re-established after recession of the flows, net primary production proved to be ~4% of the rate of photosynthesis. This result and the observed low-nutrient concentrations in the river suggest a tight coupling between photosynthetic fixation of carbon and the microbial degradation of photosynthetic products comprising plant material and exudates.

Environmental DNA detects Critically Endangered largetooth sawfish in the wild

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Diel phosphorus variation and the stoichiometry of ecosystem metabolism in a large spring‐fed river

“…Aquatic plants, including algae and other microbial primary producers, are notoriously leaky, losing large quantities of assimilated nutrients to the environment (Khailov and Burlakova 1969, Larsson and Hagstrom 1979, Descy et al 2002, Webster et al 2005. If material exuded by primary producers in the Ichetucknee River differs in elemental composition from standing biomass, as has been observed in other systems (e.g., transparent exopolymers with high C:N; Passow 2002), then our expectation that ecosystem and organismal stoichiometry will match is invalid.…”

The effects of storm-induced events on the seasonal dynamics of epilithic algal biomass in subtropical mountain streams

“…Because most natural and pristine streams or rivers around the world are shallow with low nutrient concentrations, a high canopy cover, and low phytoplankton biomass, light-limited benthic algae tend to dominate primary production. Light availability is commonly reported to be the dominant limiting factor, rather than nutrients or temperature, in stream and river ecosystems, especially in habitats with subsaturated irradiance (Mosisch et al 2001;Webster et al 2005). In addition to the effects of scouring floods that removed algal biomass, we found that shade from the riparian canopy cover was another key driver of algal growth at all study sites.…”

“…These influences can affect physical and biogeochemical processes, the food-web structure, and ecosystem metabolism (Webster et al 2005;Huang et al 2007;Yang et al 2009). Global warming is expected to change the spatial and temporal patterns of precipitation, to increase the intensity of storms and precipitation, and to reduce the duration of sunshine in tropical and subtropical regions (Kerr 2007;Zhang et al 2007).…”