Weathering biota

If the weathering rate equals or exceeds the rate of H+ release by the biota, such as would be the case in a calcareous soil, the soil will maintain a buffer in base cations and residual alkalinity. On the other hand, in noncalcareous "acid" soils, the rate of H+ release by the biomass may exceed the rate of H+ consumption by weathering and cause a progressive acidification of the soil. In some instances, the acidic atmospheric deposition may be sufficient to disturb an existing H+ balance... 

Because of their role as an elemental sink, the formation and weathering of evaporites has the potential to affect the salinity of seawater. This can in turn alter climate, because the heat capacity of seawater is a function of its salt content. Changes in the salt content of seawater also have the potential to affect survival of marine biota, particularly the calcifiers. 

There are various environments in which recent formation of Fe oxides on earth can be observed. Among these are active volcanoes, soils (see Chap. 16), rivers and lakes, oceans, both hydrothermal and cold springs, and biota (see Chap. 17). All these environments supply helpful information about the pathways of Fe oxide formation in the geological past of which they may be considered as present-day analogues. Since spectroscopic information about the red Martian surface became available, there has been much speculation about the possibility of past Fe oxide formation by surface weathering on Mars. 

Metals released from mines and mine sites, and in some cases from the natural weathering of ore deposits, can harm aquatic biota in adjacent water bodies (Borgmann et al., 2001). Metals are present in aqueous environments in a variety of species with various toxicities and potential for bioaccumulation. Transformations among these species depend on the physical and chemical characteristics of the waterbody. Metal toxicity can be acute... 

Fig. 8. Steady-state model for the earth s surface geochemical system. The interaction of water with rocks in the presence of photosynthesized oiganic matter continuously produces reactive material of high surface area. This process provides nutrient supply to the biosphere and, along with biota, forms the array of small particles (sods). Weathering imparts solutes to the water, and erosion brings particles into surface waters and oceans.

Key nuclear and physical transformations that and its longer-lived daughters undergo in the ocean and atmosphere are illustrated in Fig. 5.20. This cartoon is a simplification that excludes some physical sources and sinks, does not specify the chemical forms of the elements, and ignores daughters vith half lives less than a day. Like most seawater elements, is weathered out of continental rocks and carried by rivers to the ocean, where it occurs in a highly soluble dissolved form or in detrital sedimentary minerals. Because uranium is strongly complexed by CO3 ions, it is relatively inert to particle adsorption, is not readily used by marine biota, and behaves conservatively in seawater. Dissolved which does decay in... 

The fate and behaviour of oil on shorelines is influenced by many factors, some of which relate to the oil itself, some to characteristics of the shoreline, and others to conditions at the time the oil is deposited on the shoreline, such as weather and waves. These factors include the type and amount of oil, the degree of weathering of the oil, both before it reaches the shoreline and while on the shoreline, the temperature, the state of the tide when the oil washes onshore, the type of beach substrate, i.e., its material composition, the type and sensitivity of biota on the beach, and the steepness of the shore. 

Arctic environments are often cited as a special case for oil spills, but in fact, extensive work on the toxicity and effects of oil have shown that Arctic species are about equally sensitive to oiling as their southern equivalents. The impact of an oil spill is increased, however, by the fact that the diversity of biota in the Arctic is very low and it takes longer to develop and grow. As oil takes longer to degrade and weather in the Arctic, toxic, volatile components are retained longer. For all these reasons, recovery from an oil spill is slower in an Arctic environment than in temperate and tropical zones. 

The retention or removal of ions, molecules, and compounds in the weathering and soil environment depends on the nature, strength, and abundance of the proton donors. The biota directly or indirectly affects the production of the proton donors. 

The decrease in density between water and ice has a number of important implications for the world around us. Ice floats because it is less dense than liquid water. This is not true of any other liquid/solid equilibrium. Solid methane sinks in liquid methane and solid ammonia sinks in liquid ammonia. Floating ice means that ponds and lakes freeze from the top down, allowing fish and other biota to live protected from the cold weather of winter. If water froze from the bottom up, life as we know it would not have evolved on Earth. 

---