Search

We present a model of estuarine mixing, removal, and input for dissolved constituents, and apply the model to 39 nutrient (P, N, Si) profiles collected over a 14-month period in a pristine river/ estuary: Ochlockonee Bay, Florida. Each profile is deconvolved into three component functions: linear mixing (conservative) first-order removal (biological productivity), and parabolic input (regeneration). After correction for temporal variations in the fluvial end-members, the model provides quantitative estimates of total estuarine primary production, net regeneration, and subsequent fluxes to the ocean over a year-long period. The modeled data set is internally self-consistent: virtually perfect mass balances are obtained for P and Si. All biological P-uptake is regenerated within the estuary so that virtually 100% of the fluvial reactive-P enters the ocean. One-third of the fluvial reactive-P enters the estuary as particles whose phosphate is released after deposition in estuarine sediments. About 20% of the dissolved fluvial silica flux is removed biologically; all of this biogenic silica dissolves in the estuary and enters the ocean. N cannot be mass balanced, probably because it enters and escapes the bay in unmeasured forms (as NH4 or via denitrification to N2 and N2O). In the Ochlockonee, biological productivity removes nutrients in the ratios N:P ≅ 9:1 and Si:P ≅ 20:1.

Eleven monthly estuarine profiles of dissolved inorganic germanium (Gei) and silica (Si) in a natural, pristine river/bay system demonstrate that Ge-removal and -input parallel the seasonal silica cycle, reflecting Ge-uptake by and -dissolution from diatoms. The Ge/Si atom ratio of the river is 0.6 ± 0.15 × 10−6, which is near the average value for continental granites and for uncontaminated, remote, natural rivers (0.7 ± 0.3 × 10−6). The Ge Si ratio escaping this estuary to the ocean is 0.8 × 10−6, reflecting some estuarine enhancement of the fluvial Ge-flux, probably due to release of Gei from fluvial particulates. Nevertheless, the post-estuarine Ge Si ratio is not significantly different from the continental crustal ratio but is very different from the ratio in sea-floor hot springs and mid-ocean ridge hydrothermal plumes (4 ± 2 × 10−6) and in oceanic basalts (2.6 × 10−6). Thus natural estuarine processes do not obscure the contrasting Ge Si signatures entering the ocean from dissolution of continental and sea-floor silicates.