Control and Disinfection II. Optimizing Chemical Disinfections Gerry Mackie Water Systems Analysts Guelph, Ontario, Canada N1H 7B2

Optimizing Disinfection with Non-oxidative Chemical Control The key is in the timing

Key Variables for Infestations Biotic Variables The mussel’s life cycle and development rate Number of generations Adult filtration rates Adult body condition Factors affecting the larval and adult densities and development rates “Trophic variables” Chlorophyll a Abiotic Variables “Chalk” variables [Ca] pH Alkalinity Hardness “Trophic” variables [PT] [N compounds] Secchi depth Conductivity Temperature

Optimizing the use of chemicals Timing the biology of the mussels to the seasonal toxicity of the control agent Biology Larval development rate and settlement periods Adult filtration activity Adult body condition Seasonal toxicity Using 3 molluscicides as examples Matching (optimizing) seasonal sensitivity of larvae to seasonal toxicity of the molluscicide Matching (optimizing) seasonal sensitivity of adults to seasonal toxicity of the molluscicide

Key Variables for Optimization Biotic Variables [Chlorophyll a] – can be estimated from Secchi depth or [PT] Relationships between average summer Chlorophyll a levels and Secchi depth (left) and spring total phosphorous levels. Secchi depth m 2 4 6 8 5 Chlorophyll a ug/L 10 20 15 25 30 Summer Chlorophyll a ug/L 1 100 1000 Spring total phosphorous ug/L 0.1

Key Variables for Optimization Abiotic Variables “Chalk” variables [Ca], probably the most reliable & widely used Alkalinity (gives information on Ca availability) pH (< 8.2, CaH2CO3; > 8.2, CaCO3) Total hardness Temporary hardness Permanent hardness

Key Variables for Optimization Abiotic Variables “Trophic” variables [PT] when P is limiting [NT] when N is limiting Secchi depth – easiest and cheapest to measure

Key Variables for Optimization Abiotic Variables Conductivity – useful for estimating other variables [Ca mg/L] = 0.141 x conductivity (μS/cm)– 1.175 (r2 = 0.88, n=3950) [(TDS) mg/L] = Conductivity µS/cm x 0.65 For waters with 10-500 μS/cm CF can vary between 0.54 and 0.96, depending on [TDS], with CF increasing from 500 – 25,000 TDS mg/L

Key Variables for Optimization Abiotic Variables Temperature Temporal (e.g. seasonal) variations Spatial variations Vertical (e.g. depth) Horizontal (e.g. Downstream)

Key Variables for Optimization Of the biotic and abiotic factors, one of the easiest to monitor is: Seasonal variations in surface temperature Timing is key: Determine when reproduction and larval development will occur (i.e. when temperatures are above 12-15oC) Determine when settlement begins and ends

Biotic Factors – What do we monitor? Life Cycle

Planktonic stages: Larval development rate Biotic factors Planktonic stages: Larval development rate Larval Density No./m3 x 104 10 15 20 25 Apr May Jun Jul Aug Sep Oct Nov Dec Jan Time Feb Mar

Benthic stages: Adult Density Biotic factors Benthic stages: Adult Density Density of New Recruits No./m2 x 103 10 15 20 25 Apr May Jun Jul Aug Sep Oct Nov Dec Jan Time Feb Mar

Benthic stages: Adult Body Condition Biotic factors Benthic stages: Adult Body Condition Dry tissue weight (mg) Apr May Jun Jul Aug Sep Oct Nov Dec Jan Time Feb Mar

Benthic stages: Adult Filtration Rate Biotic factors Benthic stages: Adult Filtration Rate Filtration Rate Ml/hr/indiv. Apr May Jun Jul Aug Sep Oct Nov Dec Jan Time Feb Mar

Seasonal toxicity of some toxins 48h-LC50 (mg/L) Molluscicide A Apr May Jun Jul Aug Sep Oct Nov Dec Jan Time Feb Mar

Seasonal toxicity of some toxins 48h-LC50 (mg/L) Apr May Jun Jul Aug Sep Oct Nov Dec Jan Time Feb Mar Molluscicide B

Seasonal toxicity of some toxins 48h-LC50 (mg/L) Apr May Jun Jul Aug Sep Oct Nov Dec Jan Time Feb Mar Niclosamide Ethanolamine salt Molluscicide C

Seasonal susceptibility of some toxins to toxins Apr May Jun Jul Aug Sep Oct Nov Dec Jan Time Feb Mar Molluscicide B Molluscicide A Molluscicide C

Optimizing disinfections for larvae Susceptibility to toxins Temperature oC Apr May Jun Jul Aug Sep Oct Nov Dec Jan Time Feb Mar Northern temperate states Warmer western states Larval Density Warm western states

Optimizing disinfections Susceptibility to toxins Density of New Recruits Time Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Northern temperate zone Warm western states

Optimizing disinfection wrt adult density Susceptibility to toxins Temperature Apr May Jun Jul Aug Sep Oct Nov Dec Jan Time Feb Mar Northern temperate states Warmer western states Density of New Recruits Northern temperate zone Warm western states

Optimizing disinfection wrt adult body condition Susceptibility to toxins Dry tissue weight Warm western states Northern temperate states Temperature Apr May Jun Jul Aug Sep Oct Nov Dec Jan Time Feb Mar Warmer western states

Optimizing disinfection wrt adult filtration rate Susceptibility to toxins Filtration Rate Warm western states Northern temperate states Temperature Apr May Jun Jul Aug Sep Oct Nov Dec Jan Time Feb Mar Northern temperate states Warmer western states