Anthropogenic influences

Though the hydrosphere continues to operate in response to the same forces it always has, humans have had an unmistakable role in altering some of its balances. In general, these impacts have had relatively little effect on the overall global water balance, and there is little chance that direct manipulation of the hydrosphere will alter water storage and cycling on a global basis. 

May-June runoff peaks, 2 to 2.5 times the aimual average nmoff in the 1915-1924 period prior to dam construction, were barely 1.5 times the average flow between 1985 and 1994. Meanwhile, autumn low flows during the 1985-1994 period are close to the mean annual flow, compared to low flows at about half the mean prior to river regulation. 

To this point, direct human impacts on the hydrosphere have remained restricted to the regional scale. Although they can still be important, particularly in terms of water supply, these direct manipulations of the hydrologic cycle are unlikely to affect the global water balance significantly. However, this is not to suggest that the global water cycle is immune to human influence its close ties to other physical and 

The Earth s history, and its future, are shaped not by independent events but by an intricately linked series of feedbacks and responses spanning the spectrum of physical, chemical, and biological cycles, of which the hydrologic cycle is only a part, albeit a central one. 

Baumgartner, A. and Reichel, E. (1975). The World Water Balance Mean Annual Global, Continental and Maritime Precipitation and Run-Off. Elsevier Scientific Publishers, Amsterdam. 

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Logan, J. A. (1985). Tropospheric ozone seasonal behavior, trends, and anthropogenic influences. /. Geophys. Res. 90,10463-10482. 

The obtained results allow us to advance with the basic assumption the north sector, subject to anthropogenic influence, it showed a carbon stock 23% lower than the south sector, which had less accessibility and a better state of conservation (Table 4). These differences were statistically significant (H = 11.20, p < 0.001) only for the AGB stratum, but not for the other strata studied nor for the total carbon stock. Under similar conditions of climate, soil, geomorphology, altitude, and latitude, the human influence could explain these differences, as the AGB stratum is the easiest to appropriate by humans [10,17,19, 21]. The AGB make the largest contribution in both sectors to the carbon stock (53, 55%), followed by SOC (28-31%) and finally BGB (8-10%) depending on the sector analyzed (Figure 3). 

Mason RP, Fitzgerald WF, Morel FMM (1994) The Biogeochemical Cycling of Elemental Mercury - Anthropogenic Influences. Geochim Cosmochim Acta 58 3191-3198... 

Roos-Barraclough F, Martinez-Cortizas A, Garcia-Rodeja E, Shotyk W (2002) A 14 500 year record of the accumulation of atmospheric mercury in peat volcanic signals, anthropogenic influences and a correlation to bromine accumulation. Earth Planet Sci Lett 202 435 -51... 

Sediments are important compartments for many organic contaminants in the aquatic environment, in particular for hydrophobic POPs such as PAHs and PCBs. Sediments have been recognised as important sinks for these compounds but with the reduction in levels of them in water, the question arises of whether the older highly contaminated sediments will function in the future as secondary sources of the compounds or whether burial by recent, cleaner sediment will prevent exchange with the water phase. This will depend on the strength of turbulence/bioturbation and on anthropogenic influences such as dredging. 

In aquatic environments, Spear (1981) spotlights three research needs (1) development of analytical procedures for measurement of individual dissolved zinc species, notably the aquo ion and zinc chloride, and for nondissolved species that occur in natural waters (2) separation of natural from anthropogenic influences of sediment-water interactions on flux rates, with emphasis on anoxic conditions, the role of microorganisms, and the stability of organozinc complexes and (3) establishment of toxicity thresholds for aquatic organisms based on bioaccumulation and survival to determine the critical dose and the critical dose rate, with emphasis on aquatic communities inhabiting locales where zinc is deposited in sediments. These research needs are still valid. 

All results represent regional, natural background soil concentrations unaffected by obvious anthropogenic influences such as garbage or proximity to industrial, residential or transportation sources. 

Vreca, P., Pirc, S., Sajn, R., 2001. Natural and anthropogenic influences on geochemistry of soils in the terrains of barren and mineralized carbonate rocks in the Pb - Zn mining district of Mezica, Slovenia. Journal of Geochemistry Exploration, 74, 99-108. 

Cape Grim is an ideal location to study free-radical chemistry in extremely clean conditions (Penkett et al., 1997). It frequently experiences air masses characterized by low condensation nuclei (CN) and Radon counts (<462 cm-3 and < 100 mBq m-3, respectively) with the local wind direction in the sector 190°-280°. In these baseline conditions, air has not passed over land for 5 days or more and is therefore relatively free of anthropogenic influence. Four days, which were characterised by the lowest NOx and NMHCs levels experienced during the campaign, have been selected to be representative of baseline conditions in the Southern Ocean. 

Fig. 8 Overview of natural and anthropogenic influences on runoff characteristics...

The most universal characteristic of remote regions compared to those clearly subject to anthropogenic influences is the low NOx (see Crutzen, 1995, for a review). Under these conditions, OH is generated by the photolysis of O, to O( D), followed by its reaction with water vapor, which occurs in competition with deactivation to 0(3P) ... 

Langner, J., H. Rodhe, P. J. Crutzen, and P. Zimmermann, Anthropogenic Influence on the Distribution of Tropospheric Sulphate Aerosol, Nature, 359, 712-716 (1992). 

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