OPTICAL HETEROGENEITY IN GREEN BAY1

Differences in light penetration and light attenuating components and processes are documented along 112 km of the major (NE/SW) axis of Green Bay (Lake Michigan) during a three-day cruise (May 25–27, 1982). Measurements included diffuse attenuation of downwelling irradiance (k_d), Secchi disk transparency (SD), phytoplankton pigments (chlorophyll a and phaeophytin), turbidity (T_n), and dissolved color (absorbance). The relative importance of absorption and scattering to attenuation was calculated from paired measurements of k_d and SD. Absorption and scattering coefficients were calculated; value estimates were supported by a strong linear relationship between the scattering coefficient (b) and T_n (b = 0.99 *T_n; r²= 097, n = 12). Light attenuation characteristics, including the extent of light penetration and the magnitudes and relative importance of absorption, scattering and individual attenuating components, were found to be heterogenous in space. This heterogeneity is due to the characteristics and positions of entry of fluvial discharges to the bay as they influence levels of dissolved color (Gelbstoff), phytoplankton standing crop, and inorganic particulates. Identification of key processes regulating light penetration and their potential for response to pollution control measures can aid in the development of a water quality management plan for Green Bay.     

RESOLUTION OF IMPACTS OF RUNOFF EVENTS ON A WATER SUPPLY RESERVOIR WITH A ROBOTIC MONITORING NETWORK1

A robotic water quality monitoring network is used to resolve the coupled patterns of a natural tracer, specific conductance (SC), and metrics of light scattering and turbidity for Schoharie Creek and downstream Schoharie Reservoir, with particular emphasis on the impacts of runoff events. Strong relationships between these parameters and streamflow, and the propensity for this tributary to plunge in the reservoir in summer and fall based on its lower temperature, are reported. The entry of this stream, the primary tributary, into the reservoir as a turbid density current during runoff events is depicted as distinct and vertically coincident subsurface SC minima and peaks in measures of light scattering. The magnitudes of these signatures imparted to the reservoir's water column are demonstrated to be strongly dependent on the magnitude of the runoff event. The time course of the diminishment of these signatures and longitudinal differences in turbidity within the reservoir are described. The documented patterns of SC and metrics of light scattering provided by the robotic monitoring network offer a rare opportunity to support development and testing of a turbidity model with the necessary attributes of fine temporal and spatial resolution.     

CALCIUM CARBONATE PRECIPITATION AND TURBIDITY MEASUREMENTS IN OTISCO LAKE,NEW YORK1

ABSTRACT: Calcium carbonate precipitate, known as “whiting,” forms in a large number of hard water lakes and reservoirs, and thus contributes to turbidity measurements in these systems. Here we document the occurrence of “whitings,” and the associated impact on turbidity, in Otisco Lake, New York. A simple, potentially broadly applicable, technique, measurement of turbidity before and after acidification, successfully quantified this component of turbidity in the lake. Calcium carbonate represented 32 percent of the turbidity in the upper waters of Otisco Lake for a three-month period, and at times was as much as 70 percent. Routine monitoring of this component of turbidity in raw water sources, where it is significant, should provide insight into water quality management and treatment plant operations.     

MODELING LIGHT ATTENUATION,SECCHI DISK,AND EFFECTS OF TRIPTON IN SENACA RIVER,NEW YORK,USA1

The development, testing, and application of a probabilistic model framework for the light attenuation coefficient for downwelling irradiance (K_d) and Secchi disc transparency (SD) that resolves the effects of several light attenuating constituents, including phytoplankton and nonliving particles (tripton), is documented. The model is consistent with optical theory, partitioning the magnitudes of the light attenuating processes of absorption and scattering according to the contributions of attenuating constituents as simple summations. The probabilistic framework accommodates variations in the character and concentrations of these constituents and ambient conditions during measurements, and recognizes a linear relationship between the magnitudes of absorption and scattering by tripton. The model is tested and applied for a 21 km reach of the Seneca River, New York, that features optical gradients caused by an intervening hypereutrophic lake and dam, and a severe infestation of the exotic zebra mussel. The model is applied to resolve the roles of phytoplankton and tripton in regulating measured longitudinal patterns of SD along the study reach of the river and increases in SD since the zebra mussel invasion, and to predict decreases in K_d since the invasion.     

TURBIDITY SUSPENI)ED SEDIMENT,AND WATER CLARITY: A REVIEW1

ABSTRACT: Suspended sediment causes a range of environmental damage, including benthic smothering, irritation of fish gills, and transport of sorbed contaminants. Much of the impact, while sediment remains suspended, is related to its light attenuation, which reduces visual range in water and light availability for photosynthesis. Thus measurement of the optical attributes of suspended matter in many instances is more relevant than measurement of its mass concentration. Nephelometric turbidity, an index of light scattering by suspended particles, has been widely used as a simple, cheap, instrumental surrogate for suspended sediment, that also relates more directly than mass concentration to optical effects of suspended matter. However, turbidity is only a relative measure of scattering (versus arbitrary standards) that has no intrinsic environmental relevance until calibrated to a ‘proper’ scientific quantity. Visual clarity (measured as Secchi or black disc visibility) is a preferred optical quantity with immediate environmental relevance to aesthetics, contact recreation, and fish habitat. Contrary to common perception, visual clarity measurement is not particularly subjective and is more precise than turbidity measurement. Black disc visibility is inter‐convertible with beam attenuation, a fundamental optical quantity that can be monitored continuously by beam transmissometry. Visual clarity or beam attenuation should supplant nephelometric turbidity in many water quality applications, including environmental standards.     

PRECIPITATION CHANGES FROM 1956 TO 1996 ON THE WALNUT GULCH EXPERIMENTAL WATERSHED1

ABSTRACT: The climate of Southern Arizona is dominated by summer precipitation, which accounts for over 60 percent of the annual total. Summer and non‐summer precipitation data from the USDA‐ARS Walnut Gulch Experimental Watershed are analyzed to identify trends in precipitation characteristics from 1956 to 1996. During this period, annual precipitation increased. The annual precipitation increase can be attributed to an increase in precipitation during non‐summer months, and is paralleled by an increase in the proportion of annual precipitation contributed during non‐summer months. This finding is consistent with previously reported increases in non‐summer precipitation in the southwestern United States. Detailed event data were analyzed to provide insight into the characteristics of precipitation events during this time period. Precipitation event data were characterized based on the number of events, event precipitation amount, 30‐minute event intensity, and event duration. The trend in non‐summer precipitation appears to be a result of increased event frequency since the number of events increased during nonsummer months, although the average amount per event, average event intensity, and average event duration did not. During the summer “monsoon” season, the frequency of recorded precipitation events increased but the average precipitation amount per event decreased. Knowledge of precipitation trends and the characteristics of events that make up a precipitation time series is a critical first step in understanding and managing water resources in semiarid ecosystems.     

WHAT DO WE MEAN BY “METROPOLITAN WATER MANAGEMENT INSTITUTIONS?”1

ABSTRACT The term “institution” and several variants are used frequently in the literature on metropolitan water management. The state-of-the art investigation on which this paper is based revealed that 1) many uses of the term do not include careful definitions; 2) many users of the term seemed unaware of the general, theoretical literature on the subject of institutions; 3) there was little consistency among uses, either in the practical literature dealing with water or in the conceptual literature dealing with theories of institutions or institutionalization; 4) some usages were without significant meaning; 5) in many cases the term was used as a kind of “black box” to account for behavioral, societal, or managerial factors; 6) the term was often used as a synonym for “organization”. This latter use is frequently found in federal reports, including National Water Commission studies, and is most unfortunate because it tends to slight significant social-psychological factors. A suggested definition is: “An institution is the structured result or outcome of a process by which values are articulated, arranged, and communicated, having continuity over time, and influencing behavior of persons who did not necessarily participate in formulating those values (norms).”     

MATHEMATICAL MODEL OR “CURVE FIT” - TELL IT LIKE IT IS1

A very fashionable term in present day engineering is mathematical model. A term which has grown into somewhat ill-repute is “curve fit.” The basic purpose of this paper is to discuss the difference between a mathematical model and a “curve fit.” In addition, a discussion of proof testing of both “curve fits” and mathematical models will be presented, followed by a brief discussion of the form and of the uses of “curve fits” and mathematical models.     

Tributary Plunging in an Urban Lake (Onondaga Lake): Drivers,Signatures, and Implications1

Abstract: A combination of long‐term fixed‐frequency and robotic monitoring information for a polluted urban lake, Onondaga Lake, New York, and two of its tributaries is used to resolve the propensity for, and occurrences of, tributary plunging. Cooler temperatures (T) and higher salinity (S) are primarily responsible for the elevated density and plunging of one of these polluted streams for the summer through early fall interval. In‐lake transport of this plunging tributary, which receives inputs from combined sewer overflows (CSOs), is tracked by its high S during dry weather, its high turbidity (T_n) with associated lower S (dilution with rainwater) following runoff events, and by its characteristic ionic composition. These signatures are documented extending from the creek mouth, through a connecting navigation channel, through the inflow zone of the lake, and into metalimnetic depths of pelagic portions of the lake. The entry of this polluted tributary below the depth interval(s) of primary production and contact recreation has important implications for the ongoing major rehabilitation program for this lake. The plunging phenomenon diminishes the benefits previously expected for related features of the lake’s water quality from ongoing management efforts to abate CSO inputs and reduce nonpoint nutrient loading from the tributary. Previously this tributary tended to instead enter the upper layers of the lake during the operation of an adjoining soda ash manufacturing facility (closure in 1986), as a result of high lake S caused by the industry’s ionic waste discharge.     

ANALYSIS OF HYDRILLA-INHIBITING FRACTIONS IN NATURAL WATERS: THE CONCEPT OF “FINGERPRINTING” THROUGH LIQUID CHROMATOGRAPHY1

ABSTRACT: High performance liquid chromatography (HPLC) has been used to identify a fraction of aqueous sediment extract from Lake Starvation, Hillsborough County, Florida, that is responsible for inhibition of hydrilla growth. The fraction was separated on a Zorbax? C₁₈ preparative-scale column. The present study examines various lake sediment extracts and river water samples to determine the presence or absence of the inhibitor peak. The biologically active component is absent in certain rivers where hydrilla is prominent, but it is present in extracts of Lake Starvation and White Trout Lake sediments that are known to have hydrilla growth inhibiting properties. The implications of “fingerprinting” natural waters for hydrilla inhibitor through liquid chromatography are considered.     

CAUSES OF UGHT AVI'ENUATION IN TAMPA BAY AND CHARLOTTE HARBOR,SOUTHWESTERN FLORIDA1

ABSTRACT: Vertical attenuation of photosynthetically active radiation (PAR) in clear waters of central Florida theoretically can vary almost 50 percent during a sunny summer day as a result of changing solar elevation. We used a simple formula to partially adjust the attenuation coefficient in Tampa Bay and Charlotte Harbor for changing solar elevation of the direct beam and then used multiple regression analysis to estimate the relative contribution of different water properties or constituents to the adjusted attenuation coefficient, k_adj. Color, on an average, was responsible for 18 percent of k_adj, chlorophyll a for 21 percent, nonchiorophyll suspended matter for 55 percent, and seawater for the remaining 6 percent. In both estuaries, k_adj increased with decreasing salinity as a result of freshwater runoff adding color, suspended matter, and nutrients. Nutrients affected attenuation by stimulating phytoplankton growth and increasing concentrations of chlorophyll a. Reduced nutrient loading to upper Tampa Bay (Hilisborough Bay) in the early to mid-1980's appears to have decreased concentrations of chlorophyll a, increased water clarity, and increased seagrass recolonization. Assuming other attenuating substances remained unchanged, the decrease in the average concentration of chlorophyll a from 30 to 15 μg L_?1 would correspond to an increase in the depth of light penetration necessary for seagrass survival (>10 percent incident light) from 1.0 to 1.5 m, which, on a relatively flat sea bed (slope of 2 m/km), would increase the area potentially available for seagram recolonization by 0.25 km²/km of shoreline.     

WATER QUALITY IN AGRICULTURAL WATERSHEDS: IMPACT OF RIPARIAN VEGETATION DURING BASE FLOW1

ABSTRACT: Water quality was monitored for 17 months during base flow periods in six agricultural watersheds to evaluate the impact of riparian vegetation on suspended solids and nutrient concentrations. In areas without riparian vegetation, both instream algal production and seasonal low flows appeared to be major determinants of suspended solids, turbidity, and phosphorus concentrations. Peak levels of all parameters were reached during the summer when flows were reduced and benthic algal production was high. Similar summer peaks were reached in streams receiving major point inputs but peaks occurred downstream from the input. Instream organic production was less important in regulating water quality in areas with riparian vegetation and permanent flows. Concentrations of suspended solids remained relatively constant, while phosphorus and turbidity increased in association with leaf fall in autumn. Intermittent flow conditions in summer increased the importance of instream organic production in controlling water quality, even when riparian vegetation was present. Efforts to improve water quality in agricultural watersheds during base flow should emphasize maintenance of riparian vegetation and stable flow conditions.     

SUSPENSOIDS IN NEW YORK CITY'S DRINKING WATER RESERVOIRS: TURBIDITY APPORTIONMENT1

ABSTRACT: The technique of i ndividual p article a nalysis conducted by s canning electron microscopy interfaced with a utomated X ‐ray microanalysis (IPA/SAX) was used to characterize suspended particulate matter in New York City's drinking water reservoirs and their tributaries. The study covered a two year period and involved analyses of more than 300 samples. The particle cross sectional area per unit volume (PAV), or area concentration, was measured to account for the observed turbidity, a representation of light scattering property of the studied medium. A simple linear model with a nearly zero intercept was able to explain more than 85 percent of the variation in the measured turbidity. Moreover, the particle assemblage was categorized into generic particle types with distinctive geochemical or geological origins. Thus, PAV compositions in terms of particle types could be apportioned into turbidity components based on the model. Inorganic tripton, dominated by aluminosilicate (clay) and silicate of nonbiological nature, was found to be the major turbidity causing constituent in most cases. With the exception of one reservoir where organic detritus was significant, the predicted inorganic particle turbidity agreed with the measured turbidity within experimental error.     

The Arkansas Valley “Super Ditch”— An Analysis of Potential Economic Impacts1

McMahon, Tyler G. and Mark Griffin Smith, 2012. The Arkansas Valley “Super Ditch”— An Analysis of Potential Economic Impacts. Journal of the American Water Resources Association (JAWRA) 00(0):000‐000. 1‐12. DOI: 10.1111/jawr.12005 Abstract: In Colorado’s Arkansas River basin, urban growth and harsh farming conditions have resulted in water transfers from agricultural to urban uses. Several studies have shown that these transfers have significant secondary economic impacts associated with the removal of irrigated land from production. In response, new methods of sharing water are being developed to allow water transfers that benefit both farm and urban economies, compared with previous permanent transfers that negatively impacted surrounding farm communities. One such project currently under development is the Arkansas Valley “Super Ditch,” which is a rotational crop fallowing plan based on long‐term water leasing designed to provide an annual supply of 25,000 acre‐feet of water (31.6 Mm³). This article analyzes the net benefits of implementing the “Super Ditch” for both the farmers and the surrounding community.     

Irrigation Reliability Under Climate Change Scenarios: A Modeling Investigation in a River‐Based Irrigation Scheme in New Zealand1

Srinivasan, M.S., J. Schmidt, S. Poyck, and E. Hreinsson, 2011. Irrigation Reliability Under Climate Change Scenarios: A Modeling Investigation in a River‐Based Irrigation Scheme in New Zealand. Journal of the American Water Resources Association (JAWRA) 47(6):1261–1274. DOI: 10.1111/j.1752‐1688.2011.00568.x Abstract: The impact of climate change (CC) on irrigation reliability in a river‐based irrigation scheme in New Zealand was investigated. Reliability was defined as the river’s ability to meet the demand. Two future periods were considered, 2030‐49 (“2040”) and 2080‐99 (“2090”), and reliability at these periods were compared against those in 1980‐99 (“current”). A hydrology model, calibrated and validated for current condition, was applied to simulate flows for CC scenarios. Annual precipitation and mean temperatures were predicted to increase under CC scenarios over current condition. Occurrence of high intensity rainfall events indicated large flows under CC scenarios, though these increases could be occurring outside the irrigation season (September‐April). Compared to current condition, under CC scenarios, the number of days per season supply falling below demand could increase by 5 (2040) to 17% (2090). Snow storage plays a major role in sustaining flows in early spring under current condition. However, with increasing temperatures under CC scenarios, the average annual snow water storage could decrease from 155 mm (current) to 97‐134 mm (2040) and 40‐90 mm (2090). Under CC scenarios, to sustain the current levels of land and water uses in this scheme, storage options need to be explored.     

ASPECTS OF THE UNDERWATER LIGHT FIELD OF EIGHT CENTRAL NEW YORK LAKES1

ABSTRACT: The underwater light field of eight central New York lakes, which represent a wide range of trophic state, was characterized through paired measurements of Sechi disc transparency (SD, m) and diffuse light attenuation (K_d, m^?1). A total of 90 paired measurements are included in the data base. Substantial variability in the K_d SD product with time within individual systems, and amongst systems, was observed, which indicates differences in the relative contributions of absorption and scattering to attenuation. More than 50 percent of the temporal variability in K_d was attributable to attendant variations in chlorophyll a (C, mg m^?3) in only two of the lakes. Estimates of the adsorption (a, m^?1) and scattering (b, m^?1) coefficients based on paired K_d and SD measurements compared well with more precise determinations available for one of the lakes. Determinations of a and b for the eight lakes, from SD and K_d measurements, indicated great system-specificity and temporal variability in these characteristics. The temporal variability in relative contributions of a and b to K_d is consistent with covariation of different attenuating components and the lack of correlation between C and K_d in most of the study lakes.     

Resolution and Analysis of Spatial Variations and Patterns in an Urban Lake with Rapid Profiling Instrumentation

Rapid response vertical profiling instrumentation was used to document spatial variability and patterns in a small urban lake, Onondaga Lake, associated with multiple drivers. Paired profiles of temperature, specific conductance (SC), turbidity (T_n), fluorometric chlorophyll a (Chl_f), and nitrate nitrogen (NO₃^?) were collected at >30 fixed locations (a “gridding”) weekly, over the spring to fall interval of several years. These gridding data are analyzed (1) to characterize phytoplankton (Chl_f) patchiness in the lake's upper waters, (2) to establish the representativeness of a single long‐term site for monitoring lake‐wide conditions, and (3) to resolve spatial patterns of multiple tracers imparted by buoyancy effects of inflows. Multiple buoyancy signatures were resolved, including overflows from less dense inflows, and interflows to metalimnetic depths and underflows to the bottom from the plunging of more dense inputs. Three different metrics had utility as tracers in depicting the buoyancy signatures as follows: (1) SC, for salinity‐enriched tributaries and the more dilute river that receives the lake's outflow, (2) T_n, for the tributaries during runoff events, and (3) NO₃^?, for the effluent of a domestic waste treatment facility and from the addition of NO₃^? solution to control methyl mercury. The plunging inflow phenomenon, which frequently prevailed, has important management implications.     

A disaggregated emissions inventory for Taiwan with uses in hybrid input‐output life cycle analysis (IO‐LCA)

This paper reports on a life‐cycle analysis (LCA) of Taiwan's “agriculture and forestry”, “crude petroleum, coal and natural gas extraction” and “electricity generation” sectors, revealing for the first time Taiwan's CO₂ and CH₄ emissions inventories and matching Taiwan's input‐output sectors. Integrated hybrid input‐output life cycle analysis is used to disaggregate the electricity generation sector into nuclear, hydro, gas, oil and coal, and cogeneration. Results show that the fossil‐fuel‐related electricity sub‐sectors have higher CO₂ emissions intensity than the remaining sectors in the economy and that the “paddy rice” sector is Taiwan's most CH₄‐intensive sector, making rice cultivation an important source of CH₄ emissions. This work is vital to sound policy decisions concerning power generation, coal, and agriculture and forestry at the national level.     

ESTIMATION OF OPTICAL PROPERTIES OF WATER FROM SECCHI DISK DEPTHS1

ABSTRACT: Optical information on a water body is often required when only Secchi disk depths are available. Many limnologists and water managers have attempted to estimate diffuse light attenuation in water from Secchi depth data assuming a simple inverse relationship. However, we show theoretically that the product of Secchi depth and the diffuse attenuation coefficient is markedly dependent on the reflectance coefficient (“brightness”) of water. Data from 28 New Zealand lakes of diverse optical character demonstrated this dependence over a wide range of reflectance (1.1 to 35.9 percent). Uncritical estimation of attenuation coefficients for diffuse light from Secchi depths, using the currently available simple inverse expressions, is discouraged because of the possibility of bias.