Mamberamo River Estuary, Irian Jaya

 M. Muchtar and A.G. Ilahude

Study area description

The Mamberamo River is in Irian Jaya, the Indonesian part of the West New Guinea Island, 1.6^oS, 137.9^oE.  It is 650 km long, with a catchment of about 76,000 km².  It discharges its turbid water into the narrow continental shelf and immediate, very steep continental slope of the Pacific Ocean north of the New Guinea Coast (Figure 1).

Figure 1.  Location of Mamberano River estuary, Irian Jaya.

 The river originates from the mountainous area of the island at 3,000 m altitude, so that there is quite significant slope along the river’s path to the ocean.  A heavy load of suspended matter is carried through a deeply-scoured, long canyon that extends inland about 60 miles from the river mouth.

 The mean depth at mid-estuary is 20 m, and the width of the river is about 2,500 m at the mouth and about 800 m at the river end of the estuary.  The average net river flow into the estuary is about 130x10⁶ m^-3 yr^-1.  Annual average rainfall is 3,050 mm.

 The hydrological data are presented in Table 1.  These data are from the observation in May 1999, during the ebb-tide in the estuary of the Mamberamo River.  They are at present kept at Oceanography Division.

Water and salt balance

Figure 2 shows the water and salt budgets for Mamberamo River estuary.  Using the data collected and applying the LOICZ Biogeochemical Modelling Guidelines (Gordon et al. 1996), water exchange time is estimated to be less than one day (4 hours).

 Budgets of nonconservative materials

Because of the very rapid exchange time, it is not possible to calculate reliably the nonconservative fluxes of nutrients.  Figures 3 and 4 show the estimated DIP and DIN fluxes of the system.  There is insufficient data to derive a stoichiometric calculation at this stage.

Table 1.  Hydrological data for the Mamberamo River estuary.