The influence of diet on the distribution of nitrogen isotopes in animals was investigated by analyzing animals grown in the laboratory on diets of constant nitrogen isotopic composition. 
The isotopic composition of the nitrogen in an animal reflects the nitrogen isotopic composition of its diet. The δ^(15)N values of the whole bodies of animals are usually more positive than those of their diets. Different individuals of a species raised on the same diet can have significantly different δ^(15)N values. The variability of the relationship between the δ^(15)N values of animals and their diets is greater for different species raised on the same diet than for the same species raised on different diets. Different tissues of mice are also enriched in ^(15)N relative to the diet, with the difference between the δ^(15)N values of a tissue and the diet depending on both the kind of tissue and the diet involved. The δ^(15)N values of collagen and chitin, biochemical components that are often preserved in fossil animal remains, are also related to the δ^(15)N value of the diet. 
The dependence of the δ^(15)N values of whole animals and their tissues and biochemical components on the δ^(15)N value of diet indicates that the isotopic composition of animal nitrogen can be used to obtain information about an animal's diet if its potential food sources had different δ^(15)N values. The nitrogen isotopic method of dietary analysis probably can be used to estimate the relative use of legumes vs non-legumes or of aquatic vs terrestrial organisms as food sources for extant and fossil animals. However, the method probably will not be applicable in those modern ecosystems in which the use of chemical fertilizers has influenced the distribution of nitrogen isotopes in food sources. 
The isotopic method of dietary analysis was used to reconstruct changes in the diet of the human population that occupied the Tehuacan Valley of Mexico over a 7000 yr span. Variations in the δ^(15)C and δ^(15)N values of bone collagen suggest that C_4 and/or CAM plants (presumably mostly corn) and legumes (presumably mostly beans) were introduced into the diet much earlier than suggested by conventional archaeological analysis.

Influence of Diet On the Distribtion of Nitrogen Isotopes in Animals

It is now accepted that some human-induced climate change is unavoidable. Potential impacts on water supply have received much attention, but relatively little is known about the concomitant changes in water quality. Projected changes in air temperature and rainfall could affect river flows and, hence, the mobility and dilution of contaminants. Increased water temperatures will affect chemical reaction kinetics and, combined with deteriorations in quality, freshwater ecological status. With increased flows there will be changes in stream power and, hence, sediment loads with the potential to alter the morphology of rivers and the transfer of sediments to lakes, thereby impacting freshwater habitats in both lake and stream systems. This paper reviews such impacts through the lens of UK surface water quality. Widely accepted climate change scenarios suggest more frequent droughts in summer, as well as flash-flooding, leading to uncontrolled discharges from urban areas to receiving water courses and estuaries. Invasion by alien species is highly likely, as is migration of species within the UK adapting to changing temperatures and flow regimes. Lower flows, reduced velocities and, hence, higher water residence times in rivers and lakes will enhance the potential for toxic algal blooms and reduce dissolved oxygen levels. Upland streams could experience increased dissolved organic carbon and colour levels, requiring action at water treatment plants to prevent toxic by-products entering public water supplies. Storms that terminate drought periods will flush nutrients from urban and rural areas or generate acid pulses in acidified upland catchments. Policy responses to climate change, such as the growth of bio-fuels or emission controls, will further impact freshwater quality.

https://www.tandfonline.com/doi/pdf/10.1623/hysj.54.1.101

A review of the potential impacts of climate change on surface water quality

Long-term increases in surface water dissolved organic carbon: Observations, possible causes and environmental impacts

Rates of acidic deposition from the atmosphere (‘acid rain’) have decreased throughout the 1980s and 1990s across large portions of North America and Europe1,2. Many recent studies have attributed observed reversals in surface-water acidification at national3 and regional4 scales to the declining deposition. To test whether emissions regulations have led to widespread recovery in surface-water chemistry, we analysed regional trends between 1980 and 1995 in indicators of acidification (sulphate, nitrate and base-cation concentrations, and measured (Gran) alkalinity) for 205 lakes and streams in eight regions of North America and Europe. Dramatic differences in trend direction and strength for the two decades are apparent. In concordance with general temporal trends in acidic deposition, lake and stream sulphate concentrations decreased in all regions with the exception of Great Britain; all but one of these regions exhibited stronger downward trends in the 1990s than in the 1980s. In contrast, regional declines in lake and stream nitrate concentrations were rare and, when detected, were very small. Recovery in alkalinity, expected wherever strong regional declines in sulphate concentrations have occurred, was observed in all regions of Europe, especially in the 1990s, but in only one region (of five) in North America. We attribute the lack of recovery in three regions (south/central Ontario, the Adirondack/Catskill mountains and midwestern North America) to strong regional declines in base-cation concentrations that exceed the decreases in sulphate concentrations.

Regional trends in aquatic recovery from acidification in North America and Europe

▪ Abstract Movement between discrete habitat patches can present significant challenges to organisms. Freshwater invertebrates achieve dispersal using a variety of mechanisms that can be broadly categorized as active or passive, and which have important consequences for processes of colonization, gene flow, and evolutionary divergence. Apart from flight in adult freshwater insects, active dispersal appears relatively uncommon. Passive dispersal may occur through transport by animal vectors or wind, often involving a specific desiccation-resistant stage in the life cycle. Dispersal in freshwater taxa is difficult to study directly, and rare but biologically significant dispersal events may remain undetected. Increased use of molecular markers has provided considerable insight into the frequency of dispersal in freshwater invertebrates, particularly for groups such as crustaceans and bryozoans that disperse passively through the transport of desiccation-resistant propagules. The establishment of propagule b...

https://www.jstor.org/stable/pdfplus/2678638.pdf

Dispersal in freshwater invertebrates

Several studies have highlighted an increase in DOC concentration in streams and lakes of UK upland catchments though the causal mechanisms controlling the increase have yet to be fully explained. This study, compiles a comprehensive data set of DOC concentration records for UK catchments to evaluate trends and test whether observed increases are ubiquitous over time and space. The study analysed monthly DOC time series from 198 sites, including 29 lakes, 8 water supply reservoirs and 161 rivers. The records vary in length from 8 to 42 years going back as far as 1961. Of the 198 sites, 153 (77%) show an upward trend in DOC concentration significant at the 95% level, the remaining 45 (23%) show no significant trend and no sites show a significant decrease in DOC concentration. The average annual increase in DOC concentration was 0.17 mg C/l/year. The dataset shows: (i) a spatial consistent upward trend in the DOC concentration independent of regional effects of rainfall, acid and nitrogen deposition, and local effects of land-use change; (ii) a temporally consistent increase in DOC concentration for period back as far as the 1960s; (iii) the increase in DOC concentration means an estimated DOC flux from the UK as 0.86 Mt C for the year 2002 and is increasing at 0.02 Mt C/year. Possible reasons for the increasing DOC concentration are discussed.

Trends in Dissolved Organic Carbon in UK Rivers and Lakes

The hydrogeochemistry of shallow groundwater has been characterized in the Allt a'Mharcaidh catchment in the Scottish Cairngorms in order to: (i) assess the spatial and temporal variation in groundwater chemistry; (ii) identify the hydrogeochemical processes regulating its evolution; and (iii) examine the influence of groundwater on the quality and quantity of stream flow. Shallow groundwater in superficial drift deposits is circumneutral (pH∽7·1) and base cation concentrations are enriched compared with precipitation and drainage water from overlying podzolic soils. Modelling with NETPATH suggests that the dominant geochemical processes that account for this are the dissolution of plagioclase, K-feldspar and biotite. Groundwater emerging as springs from weathered granite underlying high altitude (>900 m) alpine soils shows similar characteristics, though weathering rates are lower, probably as a result of reduced residence times and lower temperatures. Chemical hydrograph separation techniques using acid neutralizing capacity (ANC) and Si as tracers show that groundwater is the dominant source of baseflow in the catchment and also buffers the chemistry of stream water at high flows: groundwater may account for as much as 50–60% of annual runoff in the catchment. Climate and land use in the Cairngorms are vulnerable to future changes, which may have major implications for hydrogeological processes in the area. © 1998 John Wiley & Sons, Ltd.

Hydrogeochemistry of shallow groundwater in an upland Scottish catchment

Northern european lake survey, 1995

Long-term variability in the deposition of marine ions at west coast sites in the UK Acid Waters Monitoring Network: impacts on surface water chemistry and significance for trend determination

In the autumn of 1995, Finland, Norway and Sweden initiated a joint Nordic Lake Survey using standard protocols for lake selection criteria and analytical procedures. Subsequently, the project was expanded to include Denmark, Russian Kola, Russian Karelia, Scotland and Wales. The survey covers a geographic area of ca. 1 300 000 km(2); this is about 13% of Europe's total area and 28% of Europe excluding European Russia. The total number of lakes (> 0.04 km(2)) in the study area is about 155 000 and of these 5690 lakes (3.7%) were sampled in this survey. This is 3.7% of the total lake population (> 0.04 km(2)). The lake density is about 1 lake per 9 km(2), and the sampling density is 1 lake per 244 km(2). The first common evaluation of lake chemistry in northern Europe showed that the chemistry of these lakes, except those in Denmark, are characterized by low ionic strength (dilute) waters, with low concentrations of the nutrients nitrogen and phosphorus. There are general differences in the lake water chemistry between the countries, due to differences in hydrology, precipitation chemistry, hydrology, soil cover and vegetation. From western Norway, Scotland and Wales to eastern Finland and Karelia, there is a gradient from high to low precipitation (5000 to 300 mm yr(-1)) and from mountain areas with thin and patchy soils to forested areas with thick soils. These two factors are reflected in lake water chemistry with low concentrations of base cations (Ca, Mg, Na, K), alkalinity (HCO3-) and total organic carbon (TOC) in the western areas to higher concentrations in the eastern areas. An exception is high TOC levels in lakes in Scotland and Wales. Median values for base cation concentrations are three times higher in Sweden, Finland, Scotland, and Wales than in Norway, and TOC concentrations vary even more. The lakes in Denmark are influenced by a different bedrock mineralogy than in the other countries, and agricultural activities are much more intensive in their catchments. The Danish lakes generally have much higher ion concentrations and high concentrations of nitrogen and phosphorus. In Finland, Norway, Sweden, Russian Kola and Karelia, more than 50% of the lakes have low critical load (CL) values for sulfur acidity (CL < 60 meg m(-2) yr(-1)) while Scotland, Wales, and Denmark have very few lakes with low CL. The highest percentage (27%) of lakes with exceedance of critical loads for sulfur acidity (at present S-loading) is found in Norway. In Russian Kola, Sweden and Finland 17%, 9% and 9%, respectively, of the lakes are exceeded. In Scotland, critical loads for sulfur acidity are exceeded in only 1% of the total lake population, while 24% of Welsh lakes are exceeded. In total, this adds up to approximately 22 000 lakes, corresponding to 14% of the total lake population in northern Europe, where CL for sulfur acidity is exceeded.

Ron Harriman

Papers

Trends in Dissolved Organic Carbon in UK Rivers and Lakes

Hydrogeochemistry of shallow groundwater in an upland Scottish catchment

Northern european lake survey, 1995

Long-term variability in the deposition of marine ions at west coast sites in the UK Acid Waters Monitoring Network: impacts on surface water chemistry and significance for trend determination

Northern European Lake Survey, 1995 - Finland, Norway, Sweden, Denmark, Russian Kola, Russian Karelia, Scotland and Wales