River inflow

We studied the changes of the position of the boundary of the anoxic zone on the basis of data of regular observations received in the northeastern part of the Black Sea near Gelendzhik (more than 1400 stations with the results of field observations from 1989 to the present). This part of the Sea is far from the influence of the Bosporus input and Danube River inflow. Therefore the vertical structure in this region is more stable and reflects integrated , rather than local, changes of the Sea. 

The first and only detailed analysis of the terms in equation 1 for an Amazon floodplain lake was performed at Lake Calado (Lesack and Melack 1991, 1995 Lesack 1993a, 1995). Lake Calado has a BA LA ratio ranging from about 7 at high water to about 28 at low water. River water invaded the lake at the start of rising level in the mainstem, but by midrising water, lake water steadily flowed from the lake into the river, while river levels continued to rise. By the end of the water year, Lake Calado had experienced a 10 m range in water level, and local runoff had contributed 57% of the total water input, river inflow 21%, rainfall directly onto the lake... 

In principle, the diversion of water from one basin to another or the use of natural river inflows are the basic processes that lead to lake salinization. The consequences can be devastating for example, the diversion of —100% of the water from the Amu Darya and Syr Darya rivers in central Asia to grow cotton and other crops led to the desiccation of the Aral Sea, a fivefold increase in its water salinity (59 gL during 1991... 

The main mechanisms for delivery of dissolved constituents to the ocean are river inflow and atmospheric input. Formation of authigenic minerals (those minerals that form in situ) is the ultimate sink (Fig. 2.1) for these constituents. Authigenesis primarily involves precipitation of plant and animal shells, chemical reactions in sediments, and high-temperature reactions at hydrothermal regions. We begin with a brief review of the chemical reactions influencing the dissolved ion concentrations of rivers, and end with an attempt to balance the river sources with plausible sinks for the major seawater ions. 

Based on chemical measurements for river water and atmospheric particles, it is clear that river inflow is by far the most important mechanism for the delivery of dissolved major ions and elements to the ocean. This is not the case for all elements some of the trace metals such as iron and lead have important sources from atmospheric dust, but our discussion will focus on the flux of major elements to the ocean. The concentration and origin of the major ions to river water is presented in Table 2.1. Weathering of rocks on land is the origin of the cations, Na+, Mg ", Ca " and K", whereas the source of the anions Cl, SO4 and HCOj is partly from rock weathering and partly from the gases CO2, SO2 and HCl that are delivered to the atmosphere via volcanic emissions over geologic time. 

The ratio of the inventory (total amormt) of an element in the sea to its inflow (or outflow) rate at steady state (rmchanging total mass) is a measme of its reactivity. These two terms combine to form the residence time of the dissolved constituent with respect to river inflow, tr ... 

Constituent Seawater concentration (mmol kg ) Inventory (I0 mol) River water concentration (mol kg ) River inflow (lO mol y ) (lOV)... 

Many of these reactions are in the direction needed to close the marine mass balances for major ions (Fig. 2.4). The exceptions are that they supply an unnecessary additional siiik for SO4 (CaSO precipitation) and a vast additional source of K+. The additional sink for SO4 does little damage to the marine SO4 mass balance in Fig. 2.4 because its removal affects ordy Ca + and only at the level of about 15% of the Ca + riverine inflow. The hydrothermal source for K+ cannot be rationalized as easily, because there is no adequate sink in the marine environment. Research into the sources and sinks of alkali metals reveals that K+ (and other alkali metals) that are released from basalts at high temperature are reincorporated back into basaltic rock on the sea floor at low temperature. Thus, is recycled in the vicinity of hydrothermal vents. The rates of release and incorporation are uncertain enough to obscure whether the net K+ flux is into or from the ocean in these regions. It is possible that the low-temperature removal of K+ to basalt represents a net sink large enough to accommodate the river inflow. 

Hydrothermal circulation is viewed as flow of seawater with its ambient concentration into the hydrothermal zone to replace water that is heated and rises to exit on the sea floor (Fig. 2.9). Consequently, the right-hand side of Eq. (2.5) expresses the difference in Mg + concentration between seawater, [Mg +]sw. and the hydro-thermal solution, [Mg +]iiydro- In the case of Mg + the cool limb takes seawater to the hot zone, and the altered seawater rises with no Mg + left in solution at all. Since the river inflow of Mg + is about 4.5 x 10 mol y (Table 2.3), the hydrothermal flow is simply ... 

Seawater has nearly equal amounts of alkalinity and DIG because the main source of these properties is riverine bicarbonate ion, which makes equal contributions to both constituents. The processes of CaCOs precipitation, hydrothermal circulation, and reverse weathering in sediments remove alkalinity and DIG from seawater and maintain present concentrations at about 2 mmol (meq) kg . Reconciling the balance between river inflow and alkalinity removal from the ocean is not well rmderstood, and is discussed in much greater detail in Ghapter 2. 

We are not quite finished because it is necessary to evaluate our assumption at the beginning that carbon burial is neghgible compared with ocean circulation in the deep ocean DIG balance. At steady state the burial rate and river inflow rate are the same. Using the global river flow rate (Table 1.1) and DIG concentration (Table 2.3) to calculate the burial rate gives... 

Water circulates on average about 40 times through the surface ocean before it evaporates. This is consistent with the mean residence time of water with respect to river inflow of40 000 y calculated in Chapter 2 (Table 2.3). 

Implications of these results are that phosphorus removed from the surface waters as biological flux is 30-65 times more hkely to come from upwelling than from rivers (1.3-3.0 x 10 /4.6 x 10 ), indicating that ocean circulation is far more important in regulating biological productivity than river inflow. Also, only 1 in 30-65 atoms of P that rains to the deep ocean is actually buried the rest are degraded in the deep and recycled back to surface waters. This results in a residence time for phosphorus with respect to burial of 30 000-65 000 y 30-65 times the ocean circulation rate. 

The popularity of this proposal vraned because there vras not veiy strong evidence that it occurred, and fluxes suggested in the early studies of hydrothermal processes obviated the need for low-temperature reactions to balance the river inflow of Mg " and HCOJ. This has changed we now know that the flow of water through high-temperature zones of hydrothermal areas is less than previously suggested, and the importance of low-temperature reactions and flows is uncertain. 

In considering the effect of river inflows on corals in the bay, we focused on soil grains rather than salinity because the effect of low salinity due to inflows from the rivers is smaller and shorter than that of soil grains. In considering the effect of oceanic mechanical force on corals in the bay, we focused on wave height rather than tidal current because tidal full and residual currents have a smaller effect on corals than does wave height. 

These changes were thought to be either by natural climate-induced variability or by a decrease in river inflow from Europe (25). The new appearance of a suboxic zone and the increase in salinity were possibly related because the increase in salinity of the surface layer could change the rate and depth of ventilation of the pycnocline. Mixing events in other anoxic basins like Saanich Inlet, British Columbia, have been known to result in similar suboxic zones (26-28). 

Mikulski, Z., 1982. River inflow to the Baltic Sea. Polish Academy of Sciences, Polish National Committee of the IHP, University of Warsaw, Faculty of Geography and Regional Studies. 

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