Effect of nutrient loading on biogeochemical processes in tropical tidal creeks

Abstract

The effect of increased nutrient loads on biogeochemical processes in macrotidal, mangrovelined creeks was studied in tropical Darwin Harbour, Australia. This study uses an integrative approach involving multiple benthic and pelagic processes as measures of ecosystem function, and provides a comparison of these processes in three tidal creeks receiving different loads of treated sewage effluent. There were significant differences in process rates between Buffalo Creek (BC) (hypereutrophic), which receives the largest sewage loads; Myrmidon Creek (MC) (oligotrophic-mesotrophic) which receives smaller sewage inputs; and Reference Creek (RC) (oligotrophic) which is comparatively pristine.Benthic nutrient fluxes and denitrification were more than an order of magnitude higher and lower, respectively, in BC and denitrification efficiency (DE) was \10%. Pelagic primary production rates were also much higher in BC but respiration exceeded primary production resulting in severe drawdown of O 2 concentrations at night. Hypoxic conditions released oxide-bound phosphorus and inhibited coupled nitrification-denitrification, enhancing benthic nitrogen and phosphorus fluxes, leading to a build-up of excess nutrients in the water column. Poor water quality in BC was exacerbated by limited tidal flushing imposed by a narrow meandering channel and sandbar across the mouth. In contrast to BC, the effect of the sewage load in MC was confined to the water column, and the impact was temporary and highly localized. This is attributed to the effective flushing of the sewage plume with each tidal cycle. Denitrification rates in MC and RC were high (up to 6.83 mmol N m -2 day -1 ) and DE was approximately 90%. This study has identified denitrification, benthic nutrient fluxes and pelagic primary production as the biogeochemical processes most affected by nutrient loading in these tidal creek systems. Physical process play a key role and the combined influence of nutrient loading and poor tidal flushing can have serious consequences for ecosystem functioning.

Nutrient gradients in Panamanian estuaries: effects of watershed deforestation, rainfall, upwelling, and within-estuary transformations

“…The erasure of imprint from watershed land covers we report in the remote and unpopulated Panamanian systems contrasts with results from more populated and agricultural watershed-estuary system, where Borbor-Cordova et al (2006) in Ecuador, Boehm et al (2010) in Hawaii, and Smith et al (2011) in northern Australia, reported increased nutrient export from previously forested watersheds. The contrast suggests that different types of land use might indeed lead to different effects on downestuary biogeochemistry.…”

“…5, Table 4). The mid-estuary high suggested considerable release of ammonium into the water column, probably by action of ammonium regeneration from mangrove sediments (Mwa shote & Jumba 2002, Ferguson et al 2004, Alongi et al 2005, Fernandes et al 2010, Smith et al 2011, and perhaps some influence of dissimilatory nitrate reduction to ammonium (Fernandes et al 2012).…”

“…Whatever nutrient imprints emerge from contributing watersheds, we can expect that they will in turn be modified during transit in headwater streams and mangrove estuaries (Harrison et al 1997, Borbor-Cordova et al 2006, Saunders et al 2006, Smith et al 2011). These withinestuary transformations could further alter potential exports from land to sea (Dittmar & Lara 2001a,b, Dittmar et al 2001, Jennerjahn & Ittekkot 2002, Mallela & Harrod 2008.…”

Influence of cyanobacteria blooms on sediment biogeochemistry and nutrient fluxes

“…Biogeochemical pathways-The alteration of nutrient cycling pathways during cyanobacteria blooms had two primary components: increased rates of nutrient remineralization from increased biodeposition and pH enhancement of SRP and DIN effluxes. Increased labile OM deposition rates can increase rates of sediment metabolism, and cause higher rates of nutrient release, benthic oxygen consumption, and DIC production (Newell et al 2002;Smith et al 2012). With depletion of nutrients and DIC (bioavailable forms for cyanobacteria are CO 2 and HCO { 3 , O'Neil et al 2012), blooms in shallow water may benefit from the ''returned'' bioavailable nutrients and inorganic carbon after sediment decomposition (Kemp et al 2005).…”

Methane and nitrous oxide emissions from South East Queensland waterways

“…This model requires the gas concentration difference across the water and air interface along with the gas transfer velocity Upstill-Goddard 2006). To get insight in the production and consumption of GHG in the sediments, interfacial fluxes between sediment and water body can be determined using either sediment core incubations in the laboratory (Nishio et al 1982;Dong et al 2002;Qu et al 2003; or automated or manual chamber incubations in situ (Breuer et al 2000;Butterbach-Bahl et al 2004;Haese et al 2007;Smith et al 2012 . This method, which has to date only been described for the measurement of CH 4 , requires a relatively large amount of sample.…”