water samples

temperature

Water temperature affects nearly every aspect of the physical, chemical and biological processes of water. Its analysis is therefore indispensable for the interpretation of other parameters of water quality. All organisms living in water are adapted to a certain temperature range. They can tolerate fluctuations and rises in temperature only to a certain extent. For example, the maximum temperature for brown trout is 27°C while for carp it is 37.7°.

The temperature in European waters ranges between 0°C and 25°C. An increase may lead to:

• a decrease in density and viscosity (anything above 4°C); higher water temperatures enhance sedimentation of particulate matters
• an increase in the rate of gas exchange between water and atmosphere
• a decline in the solubility of gases in water. This is particularly important for oxygen concentration, and this also applies to carbon dioxide, ammonia, nitrogen and other gases.
• a growth in free ammonia, as opposed to bound ammonium, is toxic to fish
• a rise in the reaction rate of chemical processes
• a surge in the reaction rates of aerobic and anaerobic biochemical processes (e.g., carbon decomposition and nitrification).
• an uptick in the activity and metabolism of aquatic organisms
• an increase in the growth rate of aquatic organisms

ph-value

The pH value is used to measure the neutral, acidic or alkali behaviour of a solution. In pure water or neutral solutions, the pH value = 7. Lower pH values indicate an acidic while higher pH values an alkali aqueous environment. The pH scale ranges from 0 – 14.

Due to the effect of carbonic acid, humic substances and water influxes from the subsoil, the pH value of natural waters deviates from the optimal, neutral value of 7. In addition, pH value is impacted by temperature and salts. Wastewater discharges and microbial and plant transformations of wastewater constituents along with acid rain contribute to the shift in the pH value of natural waters. Generally, the pH value of natural waters varies between 6.5 and 8.5.

PH values below 5.5 means most small organisms are injured or killed. For fish, pH values that are too low or too high lead to various health conditions and diseases. Limits lethal to native fish species are values <4 and >10.8.

Long-term exceedances of the above-mentioned values, as well as transient stark fluctuations, are detrimental is a variety of ways – inhibition of metabolic processes, decimation of animal and plant species and reduced capacity in self-purification.

electr. conductivity

By setting the electrical conductivity (= reciprocal of electrical resistance) at 25°C, expressed in microsiemens per centimetre (µS/cm), a statement regarding the total concentration of dissolved salts (present as ions) may be quickly and easily obtained.

The sources of salts naturally present in waterways and of anthropogenic salt pollution are:

• geogenic origin (weathering)
• industrial discharges
• salt excretion by humans and animals
• road salt used in winter

The salt concentration in waterways is, primarily, composed of:

• cations (positively-charged ions): sodium, calcium, magnesium, potassium
• anions (negatively-charged ions): chloride, sulphate, hydrogen carbonate, carbonate and nitrate

turbidity

Turbidity in water is caused by undissolved, finely dispersed substances. These enter the water as discharged or run-off solids, or, under certain conditions, they form as plankton in the water.

Turbidity alters the light conditions in the water and thus has an impact on photosynthesis and growth of aquatic plants and planktons, especially in very slow flowing waters. Turbidity, especially plankton, can affect the oxygen balance of a body of water. In addition, turbidity can settle and affect the habitat of organisms living on the water bottom.

Turbidity measurements provide attestations of spontaneous or long-term changes in water quality with little effort, provided that undissolved substances are the root cause.

Erosion, turbulence, discharge from sewage treatment plants, rainwater and sewer outflows or material conversion in the water are the main causes of increased turbidity.

oxygen

The dissolved oxygen concentration ascertained in a body of water is the result of oxygen-consuming and oxygen-supplying processes. Oxygen concentration is a value that may quite easily be affected by processes both internal and external to the water and can therefore fluctuate greatly under certain circumstances. The state of equilibrium is represented by pressure- and temperature-dependent saturation; at a temperature of 10°, for example, an oxygen content of 10.92 mg/L corresponds to a saturation rate of 100%. Due to natural and anthropogenic influences, the oxygen concentrations of water bodies deviate from this equilibrium to a greater or lesser extent. Turbulence always causes a change in oxygen concentration towards saturation due to intensive interfacial exchange between air and water.

Due to the organisms living in the water, whose oxygen demands are variously different, there are oxygen-supplying processes (photosynthesis by green plants) and oxygen-consuming metabolic processes. Oxygen is consumed in water, especially, through aerobic decomposition of carbon compounds and nitrification of ammonium. Low oxygen concentrations indicate depletion processes by substances that have either been discharged or arisen in the water as secondary pollution (dying aquatic plants and algae). Natural oxygen supersaturation occurs only in water through photosynthesis. They are an indication of a possible hazard stemming from eutrophication processes, since periods of oversaturation are often followed by periods of reduced oxygen concentrations, depending on discharge and meteorological boundary conditions.

ammonium

Ammonium is a cation (positively-charged ions), whose various compounds are highly soluble in water. Ammonium is constantly released during biochemical degradation of discharged nitrogenous substances (e.g., proteins, amino acids, urea), though they also naturally formed biomass and is, therefore, usually present in small quantities in water bodies.

High concentrations of ammonium are the result of agricultural, domestic, municipal and industrial wastewater. Ammonium is also carried into surface waters from the atmosphere via precipitation.

Generally-speaking, ammonium in water bodies is oxidized by microorganisms (nitrifiers) via nitrite to nitrate, which can mean a serious burden on the oxygen balance.

Ammonium is in a dissociative relationship with toxic ammonia – as the pH value rises (>7) and temperature increases, the balance shifts in favour of the highly fish-toxic ammonia. Damage to fry (hatched fish) and sensitive fish species can be expected at ammonia concentrations of 0.01 mg/L; lethal concentrations are in the order of 0.2 mg/L for fry and 0.6 mg/L for trout.

In flowing waters, the fluctuations in ammonium concentration due to impact loads from sewage treatment plants and combined water discharges can be considerable (low = 0.1 mg/L, very high = 20mg/L).

nitrate

Nitrate is the anion (negatively-charge ion) of nitric acid. Nitrate compounds are highly soluble in water. In flowing waters, nitrate is mostly present as a natural metabolic product of nitrification in moderate concentrations. The main sources of nitrate pollution are the leaching of fertilizers from agricultural soils and sewage treatment plant effluents. Nitrate also enters water bodies via rainfall.

Along with phosphorus, nitrate is an important nutrient for aquatic plants and is generally so abundant that it does not usually act as a limiting factor in the eutrophication of water bodies (algal blooms, weed growth). The amount of nitrate removed by plants is insignificant in relation to the total concentration in the water body. A significant decrease in nitrate concentration on a flowing waterway occurs only during the vegetation period, which mostly involves denitrification on the sediment surface. Transient fluctuations are caused by shock loads from wastewater plants and combined sewer discharges. Nitrate is not harmful to aquatic organisms even at high concentrations of 10 mg/L.

phosphorus

Phosphorus is a vital nutrient for all organisms. Phosphorus enters surface waters through various points from diffuse, natural and, primarily, anthropogenic sources.

Phosphorus is found in excrement and used as inorganic compounds in fertilisers or as organophosphorus compounds in pesticides. Domestic, agricultural as well as industrial wastewater are therefore main sources of phosphorus inputs. Furthermore, a considerable proportion of phosphorus compounds variously enters water bodies through erosion, i.e., washed away, partly over-fertilised soil. An additional source of phosphorus input is from precipitation.

In non-polluted waters, phosphorus is naturally present, albeit, in very low concentrations, which inhibits plant growth as a minimizing factor. Anthropogenic inputs of phosphorus are the main eutrophication factor. The consequences of sufficient light supply are strong weed growth – higher submerged and emersed aquatic plants as well as filamentous algae or mass proliferation of phytoplankton (algal blooms). Excessive plant growth results most of all in diurnal fluctuations of oxygen content with supersaturations, as well as pH value rises during the day and significant oxygen deficits in the early morning hours. Dying plant masses lead to secondary pollution through sludge formation and oxygen depletion.

Natural phosphorus compounds, on the other hand, are nontoxic, while some synthetic compounds, such as those used in pesticides, are highly toxic.

microplastic

Microplastic particles were found in all analyzed samples of the Danube delta. In one liter of water 46 microplastic particles with a size larger than 105 µm (coefficient of variation (CV) = 62 %), 95 particles larger than 65 µm (CV = 53 %) and 2677 microplastic particles with a min-imum size of 20 µm (CV = 11 %) were found. With an annual average discharge of 6416 m3∙s-1 [19] this adds up to approximately 1.72∙1010 plastic particles per second (> 20 µm). The most abundant plastic polymers found were PET, PTFE, PE and PA.