Nutrient Inputs

Intuition dictates that reducing nutrient inputs, particularly phosphorus, must reduce the supportable biomass. Relationships show that sustained response cannot be effected before it can be demonstrated (i) that nutrient is exhausted at a lower concentration of algae than the existing maxima and (ii) that in situ recycling is unable to make up the shortfall. 

In the first stages of the development of an Action plan all control options are considered. In the case of lakes, this process is aided by a PC-based expert system , PACGAP, which looks at the physical and chemical characteristics of the lake to determine the most likely option for control. Once further, more detailed information has been collected on the lake s nutrient inputs and other controlling factors, amore complex interactive model can be used (Phytoplankton Response To Environmental CHange, PROTECH-2) to define the efficacy of proposed control options more accurately. This model is able to predict the development of phytoplankton species populations under different nutrient and stratification regimes. 

The Action plans will also include options for controlling nutrient inputs in the upstream catchments of affected stillwaters. These are likely to include reduction of nutrients from both point and diffuse sources and a range of different combinations aimed at reaching the target concentrations of nutrients required to achieve control in the receiving waters. 

Figure 1. Generalized nutrient balance of ecosystems in the intervals between disturbance events. Natural disturbances such as wildfires, hurricanes, and floods as well as anthropogenic disturbances such as deforestation and biomass burning can dramatically influence nutrient inputs, internal cycles, and ecosystem outputs (losses).

Fig. 10-13. The links between the cycling of C, N, and O2 are indicated. Total primary production is composed of two parts. The production driven by new nutrient input to the euphotic zone is called new production (Dugdale and Goering, 1967). New production is mainly in the form of the upward flux of nitrate from below but river and atmospheric input and nitrogen fixation (Karl et al, 1997) are other possible sources. Other forms of nitrogen such as nitrite, ammonia, and urea may also be important under certain situations. The "new" nitrate is used to produce plankton protoplasm and oxygen according to the RKR equation. Some of the plant material produced is respired in the euphotic zone due to the combined efforts...

Nutrient Inputs from Urban Wastewaters and Global... 

Merseburger GC (2006) Nutrient dynamics and metabolism in Mediterranean streams affected by nutrient inputs from human activities. PhD Thesis, Universitat de Barcelona (Spain)... 

Intensive pig production systems have shown severe negative impacts on animal health and welfare (reviewed by Borell et al., 1997 Rauw et al., 1998). Further constraints of intensive production are expected owing to the dramatic effects on environmental pollution caused by a high nutrient input... 

The stubborn requirement of the American Lawn aesthetic requires that the grass remains green throughout the season, (even at times when it is naturally dormant), and that it remain an even and emerald shade. This invariably means some form of nutrient input is necessary. 

At the opposite end of the fertility scale from ricefields are peat bogs in pluvial landscapes. Nutrient inputs come almost entirely from rainfall, and the nutrient reserves in the organic matter buffering the soil solution are small (Moore and Bellamy, 1974). The chemistry of peat bogs is therefore precarious and changes in the composition of the rainfall can have a large effect on the composition of the soil solution. 

Soil surface balance measures the differences between the input or application of nutrients entering the soil (e.g. mineral fertilisers or organic manure) and the output or withdrawal of nutrients from harvested and fodder crops. Farm gate balances measure the nutrient input on the basis of the nutrient contents of purchased material (e.g. concentrates, fertilisers, fodder, livestock, biological N-fixation) and farm sales such as meat, milk, fodder, cereals (OECD 1997). 

Organic farming standards already set a narrow range for nutrient input by restricting mineral and organic fertiliser and feedstuff input. The consumption of limited resources is comparably low. 

In remote alpine areas where anthropogenic pollution is limited, the retention of nutrients associated with trapped particles may become apparent. Case studies in two Rocky Mountain lakes (Kootenay and Arrows) indicated a reduced biological productivity, which is not compensated - as is usually the case in the European Alps -by enhanced nutrient input due to anthropogenic activities in the catchment [5]. 

Eutrophication A complex series of inter-related changes in the chemical and biological status of a water body most often manifested by a depletion of the oxygen content caused by decay of organic matter resulting from a high level of primary productivity and typically caused by enhanced nutrient input. 

Estimation of the relative effectiveness of nutrient sources can be a useful way in which to estimate their efficacy as fertilisers (Barrow 1985). The relative effectiveness of alternative nutrient sources is usually calculated by comparing the yield plateau of the response curve of the fertiliser in question to a soluble source of the same nutrients (Barrow 1985). For minerals used as nutrient inputs in organic farming systems their relative effectiveness is almost always <1 due to low solubility in soil. Organic matter inputs can also be evaluated in terms of their relative effectiveness based on their recalcitrance, but of equal importance is the extent to which they are physically protected from degradation in soil aggregates (Strong et al. 1999), which would be different in different soil types. 

Figure 13.1 Relationship between nutrient inputs and the use of synthetic compounds in organic and conventional plant production.

Variation among Sampling Sites. Dissolved humic substance samples from seven end-member environments were isolated for study. Autochthonous inputs to DOM were expected to dominate in Big Soda Lake and in Island Lake, which is a groundwater-sustained eutrophic lake in the sandhills of western Nebraska. Allochthonous inputs to DOM from a swamp environment predominate in the Suwannee River. They also dominate in the Calcasieu River in western Louisiana, but the proportion of swampland is much lower there. The Temi River is a tropical blackwater tributary of the Orinoco River in Venezuela, where allochthonous inputs dominate. The entire Sagavanirktok River basin is located north of the tree line on the North Slope of Alaska a mixture of allochthonous and autochthonous inputs was expected for the various rivers and lakes in this basin. Lastly, Hidden Lake Creek, which is the outlet of Hidden Lake on the Kenai Peninsula of Alaska, was sampled to determine if nutrient inputs from decaying salmon were contributing to primary production and autochthonous inputs to DOM. 

Fig. 4. The results of annual mass balance studies for a number of fresh and salt water wetland areas receiving different levels of nutrient input. From Nixon and Lee (in press).

As a result of their geographical circumstances and these various historical developments, many estuaries appear to be among the most heavily loaded ecosystems in the world in terms of the amount of nitrogen and phosphorus received per unit area (Fig. 5). Even the farm fields of the American corn belt do not receive the fertilization common to many estuaries, and the nutrient inputs to natural terrestrial systems and fresh waters appear to be orders of magnitude lower. There are fewer data available on the inputs of metals and other pollutants to estuaries, but the evidence at hand suggests that the delivery of heavy metals to estuaries may equal or exceed that deposited from the atmosphere on heavily industrialized urban areas and exceed that deposited on rural terrestrial ecosystems by orders of magnitude (Fig. 6). 

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