The influence of mangrove biomass and production on biogeochemical processes in the Kimberley Region, Western Australia

The physiochemical and biogeochemical properties of mangrove forests in different macrotidal coastal settings were measured. The forests were: a dense Aegiceras corniculatum forest in a ria embayment of Strickland Bay (SB1); a mature Rhizophora stylosa forest in a ria delta of the Kammergoorh River (SB2); an immature Avicennia marina stand on the steep banks of Mary Island North, off the mouth of the Fitzroy River (KS3); and a mature Avicennia marina forest at a creek mouth in Roebuck Bay, a bay with sediments dominated by carbonate deposits (BR4).Rectangular plots were marked out in each forest and plot size was determined by the area occupied by 100 trees: 48.6 m² at SB1, 324.0 m² at SB2, 600.0 m² at KS3, and 399.6 m² at BR4. Above ground biomass was estimated using previously established allometric relationships for Rhizophora stylosa and Avicennia marina. The allometric equations derived for Avicennia marina were also used for Aegiceras corniculatum, for which allometric relationships were not known. Net primary production (mmol C/m²/day) was estimated using the light interception method. Below ground fine root biomass was estimated from 3 replicate cores (1 m long x 6 cm internal diameter) in each plot. Cores were subdivided at 2 cm intervals to 40 cm and 5 cm intervals to 1 m. Roots were washed and frozen until analysis, when live and dead roots were separated using the colloidal silica method. Sediment samples were collected from the forest floor within each plot. Duplicate samples for grain size and water content were taken every 10 cm to a depth of 50 cm using 50 cc syringes with the needle ends cut off. Temperature, redox potential, and pH were measured at 2 cm intervals from duplicate cores (1 m long x 6 cm internal diameter). Samples for interstitial water were taken using the same corer. Porewater samples were obtained by cutting cores under a N2 atmosphere and squeezing sediment cakes (cut at 2 cm intervals) in a Teflon porewater apparatus. Samples were analyzed for SO4 Cl, Fe, Mn, NH4, NO2 + NO3, PO4, DOC, and Total CO2. Separate samples were analyzed for CH4. The same squeezed cakes and live and dead roots were dried, ground, and analyzed for total organic carbon (TOC), total carbon (TC), and total nitrogen (TN). TOC was measured on a Beckman TOC Analyzer, and TC and TN on a Perkin Elmer 2400 CHNS/O Series II Analyzer.Rates of iron and manganese reduction were estimated, using a core incubation method, from two sets of duplicate cores (20 cm long x 7 cm internal diameter), which were subdivided into 4 cm long sections in a N2 saturated box. Rates of sulfate reduction were measured on triplicate 2.7 cm diameter cores taken from each plot using the core injection technique. Gas (O2, CO2, CH4) and solute (Total CO2, DOC, Mn, Fe, HS-, Ca, SiOH, PO4, DOP, DON, NH4, NO2 + NO3) fluxes were measured via the glass chambers placed in replicate box core (0.027 m²) samples taken from each plot. The samples were immediately incubated on board ship in a shaded water bath maintained at ambient seawater temperature. Water used in all experiments was taken from the mangrove waterways closest to each site.Gas exchange across the air-sediment interface was measured in clear and opaque chambers to estimate benthic respiration and gross primary production during air-exposed periods (12 hours/day). Benthic respiration from submerged sediments was estimated from the total CO2 flux. An estimate of daily benthic respiration (total carbon oxidation, TCOX) at each station, taking into account the effect on sediment of roughly one-half day exposure to air and one-half day submergence, was derived by averaging the CO2 (exposed condition) and total CO2 (submerged condition) flux rates.
 Field studies were undertaken to determine the influence on sediment biogeochemistry of various ages and types of mangroves, located in different coastal settings (ria, riverine delta and a carbonate dominated bay) in a high energy environment.

Organization: Australian Ocean Data Network