EVPP 550 Waterscape Ecology and Management

EVPP 550Waterscape Ecology and Management Professor R. Christian Jones Fall 2007

Global carbon cycle includes: Photosynthesis Respiration Fossil Fuel combustion Ocean interactions Rock interactions (over long term) Water Chemistry – CO2, alk, pH

Water Chemistry – CO2, alk, pH Ice core data • Earth’s atmosphere contains relatively small amounts of CO2 as compared to O2 • But the amount has increased greatly over the past several decades • As a greenhouse gas, CO2 is a major factor in the warming of Earth surface temperatures • CO2 is also intimately involved in the carbonate-bicarbonate buffering system that controls pH in most freshwaters Direct Measurements

Carbon dioxide dissolves in water to produce carbonic acid Carbonic acid dissociates to produce bicarbonate and hydrogen ion (1st dissociation of carbonic acid) Bicarbonate dissociates to produce carbonate and another hydrogen ion (2nd dissociation of carbonic acid) CO2 + H20 ↔ H2CO3 H2CO3 ↔ HCO3- + H+ HCO3- ↔ CO3-2 + H+ Water Chemistry – CO2, alk, pH

pH = -log [H+] pH is the negative log of the hydrogen ion concentration pH = 4 means [H+] = 10-4 pH = 7 means [H+] = 10-7 pH = 10 means [H+] = 10-10 Water Chemistry – CO2, alk, pH

Water Chemistry – CO2, alk, pH • The relative amounts of carbonate, bicarbonate, and carbon dioxide-carbonic acid change with pH in a predictable manner based on dissociation equations • At high pH, carbonate dominates • At intermediate pH, bicarbonate dominates • At low pH, carbon dioxide-carbonic acid dominates

Water Chemistry – CO2, alk, pH • Alkalinity is the ability of water to resist acidification • If the carbonate-bicarbonate system is the major buffer, then pH change can be resisted as long as bicarbonate and carbonate are present since they can absorb hydrogen ions • Alkalinity = [HCO3-] + 2 x [CO3-2]

Water Chemistry – CO2, alk, pH • pH of rain in equilibrium with atmospheric CO2 is about 5.5 • Pollutants such as sulfate and NOX decrease it futher • The total amount of alkalinity in a given water body is based, not only on the input of CO2 from the atmosphere, but even more so on sources of carbonate and bicarbonate from the watershed

For some purposes we need to know the total amount of dissolved inorganic carbon (DIC) in a water body This determines the carbon available for photosynthesis and also is needed to calculate the photosynthetic rate using the C-14 method DIC = [H2CO3] + [HCO3-] + [CO3-2] Based on equations in handout, if we know pH, alkalinity, and temperature, we can derive total DIC and concentration of all forms of DIC Water Chemistry – CO2, alk, pH

Effect of photosynthesis on pH and carbonate system Effect of respiration on pH and carbonate system Psyn consumes CO2, equilibrium shifts to left resulting in consumption of H+ and increase in pH Resp releases CO2, equilibrium shift to left resulting in release of H+ and decrease in pH Water Chemistry – CO2, alk, pH CO2 + H20 ↔ H2CO3 ↔ HCO3- + H+ ↔ CO3-2 + H+

Water Chemistry – CO2, alk, pH • Vertical profiles of pH

Sources Atmosphere Soil/rocks Dissolution Weathering Sediments Measurement Total Dissolved Solids (TDS) aka Filterable Residue Gravimetric procedure Filter substantial volume of water, then evaporate filtrate until constant weight Problems: some residues are volatile and some retain water Water Chemistry – Dissolved Ions

Range: 1 mg/L to 300,000 mg/L (saturated brine) Equivalent to 0.001 – 300 ppt Fresh water: < 1 ppt Ocean: 35 ppt Great Salt Lake: 220 ppt Water Chemistry – Dissolved Ions

Conductivity Measures the ability of water to conduct an electrical current Proportional to the number of ions in solution Pure water has a very low conductance (<0.1 umho/cm = uS/cm) Conductance is a rough measure of TDS which can be calibrated more accurately for a given waterbody Conductivity Is a function of temperature so values need to be standardized to a given temperature, usually 25oC Conductivity increases by a factor of about 0.025 per oC So to get Specific Conductance (Conductivity standardized to 25oC): Cond(25oC) = Cond (T) x 1.025^(25-T) Water Chemistry – Dissolved Ions

Anions CO3-2 and HCO3- (70-75% by wt) SO4-2 and Cl- also important Cations Ca+2 (60%) Mg+2 (15-20%) Na+ (15-20%) K+ (5-10%) Alkalinity [CO3-2] + [HCO3-] Acid buffering capacity Hardness [Ca+2] + [Mg+2] Reaction to soap More soap required in hard water because Ca and Mg tie some of it up Water Chemistry – Dissolved Ions

Water Chemistry - Nitrogen • Forms • N2 = dissolved molecular nitrogen • NH4+, NH3, NH4OH = ammonia nitrogen • NO2- = nitrite ion • NO3- = nitrate ion • Organic nitrogen: includes proteins, amino acids, urea, etc.

Water Chemistry - Nitrogen • Forms • Equilibrium between ammonia nitrogen forms is a function of temperature and pH

Water Chemistry - Nitrogen • Transformations • Nitrogen fixation • N2 → reduced organic N (like amino acid) • Three groups of organisms can do this • Aerobic and anaerobic heterotrophic bacteria use organic matter as energy substrate/important in sediments • Cyanobacteria use light as energy source/important in open water/done in heterocysts/may occur in large blooms in midsummer in enriched lakes • Purple photosynthetic bacteria use light as energy source, but need anoxic conditions

Water Chemistry - Nitrogen • Transformations • Nitrogen fixation • Rate of N fixation in water column is increased during N limitation • Rate of N limitation is related to light intensity implying that light energy is driving the process

Water Chemistry - Nitrogen • Transformations • Assimilation of combined nitrogen • NH4+ → reduced organic nitrogen (like amino acid) • NO3- → reduced organic nitrogen (like amino acid) • NH4+ is energetically more favorable as it is already reduced

Water Chemistry - Nitrogen • Transformations • Proteolysis or ammonification • Organic Nitrogen → NH4+ • Proteolytic bacteria use energy released from this transformation for metabolism • Nitrification • NH4+ → NO2- • Nitrosomonas uses energy released for metabolism • NO2- → NO3- • Nitrobacter uses energy released for metabolism • Reaction occurs quickly so NO2- generally very low

Water Chemistry - Nitrogen • Transformations • Denitrification • NO3- → N2 • Anaerobic/aerobic interface habitats such as mud-water interface • Active in sediments and wetlands, may greatly deplete NO3 in groundwater

Water Chemistry - Nitrogen

Importance to organisms Nucleic acids Adenosine Triphosphate (high energy PO4 bonds) Bones and other solid inclusions Sources Erosion of igneous rocks Dissolution of phosphate-containing sedimentary rocks Guano beds, bone skeletons Human and animal waste, detergents Water Chemistry - Phosphorus

Forms of phosphorus In biological systems and in water, almost all P is in the PO4 form Can be individual PO4-3 ions or PO4 group can be combined with organic molecules, either dissolved or particulate Analytic Forms Phosphate ion aka orthophosphate aka soluble reactive phosphorus Measured on filtered samples Total soluble phosphorus Measured on filtered sample after digestion Total phosphorus Measured on whole water samples after digestion Water Chemistry - Phosphorus

Ortho-P Only directly utilizable form of inorganic P May be formed from organic P by enzymatic action Reacts with other chemicals and adsorps to particles and elements like Fe Organic P = Total P – Ortho P Often most P in lakes is tied up in organisms or detritus Can cycle between ortho-P and organic P Water Chemistry - Phosphorus

P cycle in lakes Water Chemistry - Phosphorus

P profiles in various lakes Water Chemistry - Phosphorus

Water Chemistry - Iron • Iron is a necessary requirement for all living organisms (enzyme systems) • Iron has two states • Fe+3 = ferric ion • Forms insoluble compounds • Found under oxic conditions • Fe+2 = ferrous ion • Is generally soluble • Found under anoxic conditions

Even though generally insoluble in oxic epilimnion, Fe can be held there by chelators (compounds that weakly bind it to prevent precipitation, but may give it up to cells) Water Chemistry - Iron

Generally, however, in oxic conditions Fe is found in a precipitated oxide form such as Fe(OH)3 These iron precipitates help to bind PO4 in the sediments and keep it from migrating into the water column Water Chemistry - Iron

However, when anoxic conditions set in, the Fe(OH)3 dissolves and PO4-3 can be rapidly released fueling algal growth Water Chemistry - Iron

Water Chemistry - Silicon • Required for diatioms • Removed from the water column during diatom growth and sinking • May come to limit diatom growth during the growing season

EVPP 550 Waterscape Ecology and Management