Leland J. Jackson

Instream flow needs in streams and rivers: the importance of understanding ecological dynamics

Resource managers have traditionally had to rely on simple hydrological and habitat-association methods to predict how changes in river flow regimes will affect the viability of instream populations and communities. Yet these systems are characterized by dynamic feedbacks among system components, a high degree of spatial and temporal variability, and connectivity between habitats, none of which can be adequately captured in the commonly employed management methods. We argue that process-oriented ecological models, which consider dynamics across scales and levels of biological organization, are better suited to guide flow regime management. We review how ecological dynamics in streams and rivers are shaped by a combination of the flow regime and internal feedbacks, and proceed to describe ecological modeling tools that have the potential to characterize such dynamics. We conclude with a suggested research agenda to facilitate the inclusion of ecological dynamics into instream flow needs assessments.

Paradigms of metal accumulation in rooted aquatic vascular plants

This paper reviews paradigms of metal accumulation in rooted aquatic vascular plants. Radio-tracer studies have demonstrated that root uptake from sediments with subsequent translocation to above-ground tissues is the principal pathway for metal movement. The metal concentration of rooted macrophytes is generally proportional to metal concentrations in the underlying sediments, excluding crystal lattice-bound metals. Deviations from 1:1 predictions between sediment and macrophyte metal concentrations have been shown to be correlated to variation in sediment geochemistry. Sediment pH, redox potential and organic content are three particularly important sediment variables that affect phase partitioning of metals, and their bioavailability. Metals contained within macrophyte tissues can participate in cycling within the littoral zone, or at senescence, lost to the surrounding water in a dissolved form or exported out of the lake bound to shoot fragments. Relatively little is known about the trophic transfer of macrophyte-bound metals to herbivores or algae. A better understanding of the role of rooted aquatic macrophytes in ecosystem processes is likely to be advanced by considering the fate of plant metals leaked during the summer, and those dissolved forms lost to the water column during senescence. Modeling metal accumulation in aquatic vascular plants has been restricted to empirical models that provide descriptions of general patterns.

An Introduction to the Practice of Ecological Modeling

odeling has become an important tool in the study of ecological systems,as a scan of the table of con tents of a ny major eco l ogical journ a l makes abundantly clear. A number of books have recently been published that provide excellent advice on mo del construction, building, and use (e.g.,Gotelli 1995, Gurney and Nisbet 1998, Roughgarden 1998) and add to the classic literature on mo deling ecological systems and their dynamics (e.g., Maynard Smith 1974, Nisbet and Gurney 1 9 8 2 ) . Un fortu n a tely, h owever, l i t t l e — i f a ny — of t h i s growing literature on e cological modeling addresses the motivation to model and the initial stages of the modeling process, information that beginning students would find useful. Fast computers and graphical software packages have removed much of the drudgery of creating models with a programming language and opened new avenues of model construction,use,and even misuse. There are many reasons why a student might want to consider modeling as a component of his or her education. Models p rovide an opportunity to explo re ideas regarding ecological systems that it may not be possible to field-test for logistical, political, or financial reasons. Often, learning occurs from apparently st range results and unexpected sur prises. The process of formulating an e cological model is ext remely helpful for organizing one’s thinking , bringing hidden assumptions to light, and identifying data needs. More and more,students want to “do something” with modeling but are not sure how to get started. The goals of this article are to outline issues concerning the value of ecological models and some possible motivations for mo deling, and to provide an entry point to the established modeling literature so that those who are beginning to think about using models in their research can integrate modeling usefully. We therefore envision the typical reader to be an advanced undergraduate, a beginning graduate student, or a new modeler. We first consider some of the values of models and the motivation for modeling. We then discuss the steps involved in developing a mo del from an initial idea to something that is implemented on a computer, outlining some of the decisions that must be ma de along the way. Many excellent texts and journal articles deal with the technical details of models and model construction; we do not attempt to replace this literature, but rather try to make the reader aware of the issues that must be considered and point to some of the sources we have found particularly useful. We b egin with the assumption that the reader has decided that he or she would like to “do something” with modeling as part of his or her research (Figure 1). It is important to recognize the difference between models and the modeling process. A model is a representation of a particular thing, idea, or condition. Models can be as simple as a verbal statement about a subje ct or two boxes c onnected by an arrow to represent some r elationship. Alternatively, models can be ext remely c omplex and detailed, such as a mathematical description of the pathways o f nitrogen t ransformations within ecosystems. The model ing process is the series of steps taken to convert an idea first into a conceptual model and then into a quantitative m odel . Because part of what eco l ogists do is revi s e hypotheses and collect new data, the model and the view of nature that it r epresents often und ergo many changes from the initial conception to what is d eemed the final product. The discussion that follows is organized to consider issues in a sequence similar to what a new modeler would encounter. Because individuals’ backgrounds differ, the sequence is not fixed. We map one possible route through the sorts of decisions that will most lik ely need to be considered; this course is derived from our individual experiences plus the collective knowledge o f our reviewers. We begin with conceptual models because many people, even self-labeled nonmodelers, formulate conceptual models.

Macrophyte-Dominated and Turbid States of Shallow Lakes: Evidence from Alberta Lakes

Ecosystems may exist in more than one state. This provocative ecological theory was initially developed and addressed largely through modeling studies, but over the last 2 decades a number of diverse ecosystems have been shown to display alternate states. Here I present data from 30 lakes located in a relatively limited geographic region (Alberta, Canada) to seek evidence for alternate states in shallow prairie lakes. The lakes that I surveyed fell into the following three clusters based on their turbidity and maximum depth: (a) deep, relatively clear dimictic lakes, (b) shallow clear polymictic lakes, and (c) shallow turbid polymictic lakes. The shallow lakes had similar proportions of lake bottom supporting the growth of rooted submerged macrophytes, yet the macrophyte biomass was approximately five times higher in shallow clear lakes than in shallow turbid lakes. An analysis of covariance (ANCOVA) revealed that there was a significantly higher concentration of chlorophyll per unit of dissolved phosphorus in shallow lakes classified as turbid compared to those classified as clear. A separate ANCOVA also showed that the higher turbidity in the turbid lakes was not due simply to higher chlorophyllaa concentrations; rather, it appears that increased sediment resuspension is the source of the higher turbidity seen in these lakes. Food web effects appear to be small. Although these shallow Alberta lakes contain no benthic fishes, as do many European lakes that have been observed over time, the general patterns are consistent with the theory that alternate states can exist in shallow lakes.

Empirical relationships between the element composition of aquatic macrophytes and their underlying sediments

A simple view of the role of rooted macrophytes in element cycling sees them as pumps retrieving buried elements from the sediment profile. To investigate the relationship between the elemental composition of plants and sediments, we analysed published data for 39 elements. The best general model explained 84% of the variance of the log of plant element concentration: LPE = - 0.81 + 0.90 Log Sediment Element (ug/g dry wt.) − 0.12 Sediment Organic Content (ug/g drt wt.) + 0.67 Atomic radius (nm) (r2 = 0.84; n = 39)This close relationship between the concentrations of an element in plant tissues and in the underlying sediment indicates that acquatic plants do not differ markedly in element composition from the sediments in which they grow. T-tests between mean residuals indicated that these aquatic plants do not discriminate between essential and nonessential elements. Model II regression analyses showed no difference between the slopes of the functional relationships for individual elements and that of the general model. When the elements were separated into three groups (alkali, transition and related metals, and halogens), Log Sediment Element accounted for 75–96% of the variation in LPE. Element physicochemical parameters were also significant independent variables explaining an additional 3–12% variation in LPE. The relative importance of the independent variables differed for the three groups of elements.

Presence of natural and anthropogenic organic contaminants and potential fish health impacts along two river gradients in Alberta, Canada

In the current study, 28 organic contaminants were measured, many with estrogen-like activity, in water collected from 16 sites on two rivers in the South Saskatchewan River Basin, Alberta, Canada. The compounds detected included synthetic estrogens (birth control pill compounds and hormone therapy drugs) downstream of municipal wastewater effluents and natural hormones downstream of municipal wastewater effluents and in agricultural areas. Greater concentrations of cholesterol and derivatives, phytosterols, and fecal sterols were measured at the most downstream sites, which indicates cumulative inputs of such compounds in these rivers. A native minnow (longnose dace, Rhinichthys cataractae) was sampled to assess pathophysiological responses to exposure to compounds with estrogen-like activity. Hepatic vitellogenin protein was detected in at least one adult male longnose dace from 14 of 15 sites sampled for fish. Vitellogenin was negatively correlated with hepatosomatic (r = -0.47, p < 0.001) and gonadosomatic (r = -0.44, p < 0.003) indices, which suggests potential health impacts in male longnose dace in the South Saskatchewan River Basin. The current study demonstrates that organic contaminants, many with estrogen-like activity, are distributed over hundreds of kilometers throughout the South Saskatchewan River Basin and not just downstream of major point-sources. Therefore, many activities within these basins impact water quality in the South Saskatchewan River Basin and affect endemic longnose dace populations.

Fisheries management to reduce contaminant consumption

Lake Michigan is a microcosm of global environmental issues. A history of problems has plagued the lake, arising from the wide range of human activities the basin supports. Much of Lake Michigan`s watershed is agriculturally developed, and the shoreline is dotted with major urban, industrial centers. The lake has supported important commercial shipping and fishing industries for more than a century. In the 1960s and 1970s eutrophication was a concern. More recently toxic contaminants, particularly PCBs, and invasions by exotic species, such as the zebra mussel (Dreissena polymorpha), have captured headlines. More than 200 years of development and exploitation have taken Lake Michigan far from a pristine state. The Lake Michigan fishery in intensively managed, and food web manipulation may more effectively reduce PCB exposure than cleanup activities do. Four management options are discussed in this article: trophic cascade; growth maximization; size of stocked fish; and selective species stocking. The most promising option, well supported by data is in many ways the simplist: selective stocking of species that accumulate contaminants at the lowest levels. 51 refs., 6 figs., 1 tab.

Compensatory growth responses of Potamogeton pectinatus to foraging by migrating trumpeter swans in spring stop over areas

We examined spring pond use by migrating trumpeter swans (Cygnus buccinator) to assess their short-term impact on tuber and rhizome density and biomass, and to evaluate the impact of spring foraging on summer macrophyte biomass and species composition. Trumpeter swans in the Canadian subpopulation of the Rocky Mountain population select ponds that are dominated by Potamogeton pectinatus, a macrophyte favoured for its energy-rich tubers and rhizomes. Swans significantly reduced the biomass of tubers and rhizomes present in the study ponds in spring by 24%, but there was no significant impact on overall P. pectinatus shoot density and biomass the summer following herbivory. However, there were significantly fewer small P. pectinatus shoots ( < 1.0 gD W) in used areas, and other macrophyte species (Myriophyllum exalbescens, P. zosteriformis ) were present in areas where foraging had occurred. P. pectinatus may compensate for the effects of herbivory, as the number of larger shoots (range 1.0–5.0 g DW) were similar in areas where trumpeter swans had foraged and been excluded. These larger plants likely produce the tubers that will be consumed by trumpeter swans the next spring. Pond areas out of the reach of foraging swans provide a refuge for the tubers and rhizomes, also enabling the persistence of P. pectinatus.

Basin‐wide impacts of compounds with estrogen‐like activity on longnose dace (Rhinichthys cataractae) in two prairie rivers of Alberta, Canada

Environmental compounds with estrogen- or antiestrogen-like activity can enter rivers from multiple sources, including municipal wastewater and agricultural runoff. We used longnose dace (Rhinichthys cataractae) to investigate exposure to compounds with estrogen-like activity, which we measured in water at multiple sites in the Oldman and Bow rivers (AB, Canada). We evaluated changes in vitellogenin mRNA with quantitative reverse transcription-polymerase chain reaction, then compared vitellogenin levels to sex ratios and fish performance indices to assess how exposure to compounds with estrogen-like activity affects longnose dace populations. Vitellogenin levels were elevated at least 59 to 110 km downstream of municipalities. In the Oldman River, increased vitellogenin expression and female-biased sex ratios suggest severe endocrine disruption, likely resulting from the combined impacts of municipal wastewater, agriculture, and large cattle operations within the basin. In the Bow River, municipal wastewater may be the major source of compounds with estrogen-like activity that affect longnose dace. The sex ratios were not heavily skewed, as in the more agriculturally influenced Oldman River. We detected organic contaminants in river samples at every site, but the highest concentrations were found downstream of municipalities and in areas with intense agriculture. Vitellogenin levels and sex ratios of longnose dace suggest basin-wide exposure to compounds with estrogen-like activity. Our results demonstrate that it is important to assess rivers at large spatial scales to detect fully the impacts of municipal wastewater and agriculture on fish populations.

A MASS-BALANCE ANALYSIS OF TRACE METALS IN TWO WEEDBEDS

A mass-balance approach was used to examine the role of macrophyte beds as a sink or source for 7 metals over time scales varying from two months (the growing season of the plants) to one year. During the growing season the macrophyte beds were found to be net sinks for particulate metals but were net sources of dissolved metals. During senescence, ca. 15–20% of the Al, Fe, and Mn and ca. 25–30% of the Cr, Cu, Ni and Zn within the macrophyte tissues at maximum seasonal biomass was lost to the surrounding waters in a dissolved form. The export of metals from the weeds during senescence was a very small fraction (<0.01% of Al, Fe to 3.5% of Zn) of the annual allochthonous metal loading to Fitch Bay in L. Memphremagog, Quebec. In L. Weedon however, metal export during senescence was 34% (Mn) to 57%(Cu) of the annual allochthonous load. The time estimated for the plants to recycle the metals within the rooting zone of the sediments was on the order of hundreds of years. These results demonstrate that while weedbeds are net sources of metals during the summer, only a small fraction of metals in littoral sediments are not permanently buried over the longer term.