British Columbia Mine Reclamation Symposium

Marine reclamation: recovery of the sea floor community following mine tailing discharge Taylor, Laura 1984

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Proceedings of the 8th Annual British Columbia Mine Reclamation Symposium in Victoria, BC, 1984. The Technical and Research Committee on Reclamation MARINE RECLAMATION: RECOVERY OF THE SEA FLOOR COMMUNITY FOLLOWING MINE TAILING DISCHARGE by Laura Taylor Introduction The majority of North American mining-related disturbances occur in ter- restrial environments. The variable nature of impacts associated with these perturbations has initiated extensive research, the pro- gression of which can be divided into three stages: i)       the initial impacts were investigated ii)      recovery processes in habitats disturbed by   mining  were  compared  to   natural recovery processes iii)     information resulting from stages I and 2 were used to develop and implement reclamation and mitigation practices. Increasingly, mining activities have begun to majorally affect aquatic environ- ments, with tailing disposal being the primary cause of community disruption. The rise in popularity of aquatic tailing discharge has resulted as aquatic disposal is often cheaper than land impoundment, and circumvents the problem of ground water contamination com- mon to terrestrial tailing deposits (Pedersen, 1984). In British Columbia, several mines release, or have released, tailings into aquatic systems (current examples are Amax into Alice Arm, Westmin into Buttle Lake, and island Copper into Rupert Inlet). Concern that such tailing disposal might ultimately adversely affect biota of receiving waters, prompted government and industry to imple- ment comprehensive monitoring programs. These investigative programs involved initial impact assessment of mine tailing discharge. Such studies have provided the basis for the initiation of the same research progression pursued in damaged terrestrial systems. Aquatic researchers are now faced with the challenge of completing this process by in- vestigating community recovery patterns (stage ii), to provide essential ecological in- formation necessary for the development of aquatic reclamation and mitigation practices (stage iii). In 1982, a study was initiated to ex- amine benthic colonization of mine tailings in Rupert Inlet, Vancouver Island. This research, currently in progress, is a co-operative pro- ject with the author and Island Copper-Utah Mines. Island Copper employs a submarine tailing disposal system to minimize impact on primary productivity of pelagic communities in the photic zone. The success of Island Copper's submarine disposal has resulted in this methood being the preferred technqiue for aquatic tailing discharge. Submarine re- lease of tailings primarily affects bottom communities by reducing numbers of indi- viduals and/or changing community structure (Island Copper Annual Reports, 1972-1982). Therefore, this investigation focuses upon marine benthic colonization of mine tailings, as this is the biological recovery process in the disturbed system. The primary research objective is to provide essential ecological information critically necessary for develop- ment of reclamation and mitigation practices for marine benthic communities affected by tailing discharge. Impacts of Mine Tailing Discharge Upon Benthic Communities — Brief Review I.       Impact Assessment - Ongoing Mine Tailing Discharge Information currently available on sub- marine tailing release concerns effects oc- curring while discharge is continuing (Island Copper Annual Reports, 1972-1982). Biolog- ical effects include reduction in numbers of organisms, and changes to community struc- ture and composition (Island Copper Annual Reports, 1972-1982). These biotic disturb- ances are affected principally by alterations 63 Proceedings of the 8th Annual British Columbia Mine Reclamation Symposium in Victoria, BC, 1984. The Technical and Research Committee on Reclamation to four physical parameters: i) high sedimentation rates can smother existing benthos and prevent larval settlement ii) an unstable substrate may be created, thus rendering the bottom uninhabitable to many benthic organisms iii) tailing deposition can alter sediment particle size, organic and inorganic content, all of which affect benthic communities iv) accumulation of tai l ings may be so great that bottom depth is decreased, which can change benthic species com- position. The relative importance of these four factors in altering benthic community structure has not been elucidated. Clearly, the significance of each factor in deter- mining community structure will be deter- mined by physical and chemical environments of receiving waters. In Rupert Inlet, benthic organisms are known to be affected by the first two factors (Island Copper Annual Reports, 1972-1982). The third and fourth may also play a role in Rupert Inlet, however, the extent of their influence has not been examined. To determine the precise biolog- ical mechanisms through which initial impact is effected, and their relative importance, studies are now being directed to examine benthic community dynamics in disturbed and undisturbed systems. The information de- rived will be particularly useful in develop- ment of mitigation procedures for marine tailing disposal operations. 2.       Impact Assessment - Colonization Upon ceasation of mine tailing dis- charge, impact upon resident benthic com- munities will primarily be caused by the presence of a tailing substrate and its affect upon local water quality. These perturbations will mainly affect benthic colonization and community development. As the widespread use of aquatic tailing disposal is a relatively new phenomenon, investigations into dis- ruptions to community development following tailing discharge are in an early stage. Colonization proceeds through a com- mon successional pattern in terrestrial and aquatic systems (Figure I). Initially, new space is invaded by opportunistic species. These are characterized by short life cycles and rapid growth of individuals and popula- tions (Odum, 1969). Typically, these organ- isms modify their environment, enabling other species to inhabit the area. Gradually, opportunists are replaced through compe- tition and predation by an intermediate group with less rapid growth and longer life cycles. These, in turn, change their environment, giving way to equilibrium species which are long-lived and slow-growing (Odum, 1969). This final community persists as long as the system is not disturbed. Disturbance results in the community shifting back to an earlier stage in succession. The time required to reach an equilibrium community is extremely variable and is dependent upon a multitude of factors in the surrounding environment. Research Objectives The aim of this study is to examine the processes involved in benthic colonization of mine tailings, to provide ecological data for use by government and industry in develop- ment  of  management  practices.  To  clearly delineate the inquiry, the research objective has been divided into four categories: i)       what species colonize tailings? ii)      what    is    the    sequential  pattern    of species as the  community develops?  iii)  at what rate does colonization   occur?  iv)  what  affects  the  colonization   process (specifically  —  how   does   seasonality affect colonization)? If these four questions are related to the island colonization curve (MacArthur and Wilson, 1967) (Figure I), their place in the colonization process is clarified. The first question translates to an examination of the species composition on the y axis. Assess- ment of changes in species composition along the curve addresses question two. Question three involves determining the slope of the curve. Elucidation of factors that change curve shape, or species composition would 64 Proceedings of the 8th Annual British Columbia Mine Reclamation Symposium in Victoria, BC, 1984. The Technical and Research Committee on Reclamation  Figure 1 The island colonization curve of MacArthur and Wilson (1967) over time number of species increase until a dynamic equilibrium is reached 65 TIME    # of Species Proceedings of the 8th Annual British Columbia Mine Reclamation Symposium in Victoria, BC, 1984. The Technical and Research Committee on Reclamation answer question four. A multitude of factors could potentially change curve shape. There- fore, this study is limited to the examination of only one of these — the effect seasonality has on colonization. Throughout all these investigations, colonization processes in tail- ings and control sediments will be compared to determine if there are factors unique to mine tailings, that affect benthic colon- ization. Methodology I.       Rational Colonization processes can be studied in situ after disturbances denude habitats or when new space is created (Leppakoski, 1969; Simon and Dauer, 1977). For example, when a volcanic island is born or when anoxia ex- cludes most marine life from an area. Such situations are quite rare. This has led to the development of two experimental approaches to observe colonization: i)  all organisms are removed from a  site and colonization monitored  (Simberloff and Wilson, 1969) ii)       an artificial substrate is introduced into  a region, and the course of  colonization followed (Schoener, 1974;  Cairns, 1982). When employing the first method, it is often impossible to remove all organisms, and in some instances may involve habitat des- truction. If these problems are insurmount- able, artifical substrates can be utilized. This later technique has the advantage of allowing researchers to control numerous variables while still exposing organisms to the com- plexities of the field environment. Monitoring benthic colonization and succession of existing mine tailings in Rupert Inlet is not possible as Island Copper Mine is currently discharging tailings and proposes to do so for at least another twelve years. 40,000 tons of tailings are released per day, which have covered most of the Rupert Inlet seafloor (Island Copper Annual Reports, 1972- 1982). Tailings are released at a depth of 50 m, where they form a turbidity current that moves away from the outfall pipe. The position of this current within the water column is not static, rather it moves in an apparently random manner. Sedimentation rates, therefore, vary both spatially and tem- porally, thus colonizing communities may be disturbed to varying degrees at any time. Since uninterrupted benthic colonization can- not be followed in situ, an experimental ap- proach was necessary. Artifical substrates were chosen, as they allow control of select- ed variables, and as removal of all organisms from a soft substrate is impossible without habitat destruction. Many types of artificial substrates have been used in marine and fresh water systems (Cairns, 1982). The majority of these have been hard substrates, either plates or solid objects, such as rocks, enclosed in mesh bags. Previous soft bottom colonization studies (Sarnthein and Richter, 1974; McCaII, 1978; Grassle, 1980) have utilized enclosures con- taining sediment, only open at the top, to allow larval and spore settlement. Such a design potentially precludes adult recruit- ment from neighbouring communities. Since adult migration plays an important role in colonization of other systems (Simberloff and Wilson, 1969), it should not be ignored in bottom communities. 2.       Field Program An artificial substrate containment sys- tem was designed, consisting of a 0.25 m plywood box filled to a depth of IO cm with tailings (experimental), or fine white marble sand (control). Each box had only three sides, allowing adult immigration along one end. Once every two months, experimental units, consisting of two experimental and two con- trol boxes, were placed on the bottom of Rupert Inlet. These units were left in place for I, 2, 4, 8, and 12 months (Figure 2). This permitted examination of community devel- opment through time, together with seasonal variability. The artificial substrate containment system was frozen to eliminate sediment loss while lowering through the water column. Retrieval was accomplished by S.C.U.B.A. divers who secured the integrity of the 66 Proceedings of the 8th Annual British Columbia Mine Reclamation Symposium in Victoria, BC, 1984. The Technical and Research Committee on Reclamation  Figure 2 Experimental design for benthic colonization studies Each line represents a set of artificial substrate boxes. The length of the line indicates the duration of exposure of the set. Arrows show the time of retrieval. 67 Proceedings of the 8th Annual British Columbia Mine Reclamation Symposium in Victoria, BC, 1984. The Technical and Research Committee on Reclamation containment system by attaching lids to each box, which minimized sediment loss. At the surface, boxes were randomly cored and samples sieved. The field program termin- ated in August 1983. Species identification and data analysis are currently in progress. 3.       Problems Encountered in Field Experiments The major problem arising during field sampling was the loss of several experimental units. High winds and waves caused move- ment or disappearance of marker buoys des- ignating location of experimental units. This, together with extremely high turbidity (poor visibility when diving during placement and removal operations), sometimes made units impossible to find. Disruption of field prog- rams and loss of samples and equipment is by no means uncommon when conducting marine investigations. However, loss of experiment- al units could be reduced in future research by fastening marker buoys more securely, and by devising a box relocation technique that did not require visual identification. Another problem that emerged upon termination of sampling, was that sediment- ation from the water column changed heavy metal concentrations in artificial substrates. Over time, control boxes were becoming con- taminaled by sedimentation, while heavy metal levels in experimental boxes were being reduced. This change in heavy metal content was probably concentrated at the substrate surface. It is this surface layer that settling larvae perceive, so a change in this upper layer may influence larval settle- ment. Therefore, given sufficient time, com- munities in control and experimental boxes may converge as the environments become functionally similar. Sedimentation may rapidly change ben- thic environments once tailing discharge ceases. Presently this remains untested, which demonstrates the drawbacks inherent in extrapolations from experimental to natur- al conditions, and from the situation at one location to another. Ideally, investigations should be implemented in the environment under study, i.e. for this research, an examination of in situ benthic colonization in a system where tailing discharge had recently terminated. Unfortunately, such environm- ents are not always available when answers are required. Currently, Amax on Alice Arm has ceased tailing discharge, thus providing a unique opportunity for in situ examination of benthic colonization. Hopefully, studies will be done in this area, as they would undoubt- edly supply valuable information to the field of benthic colonization research. Possible Results Benthic colonization of mine tailings could proceed along a number of paths. A tailing substrate may not affect colonization. Alternately, colonization and succession may be slowed, although the eventual equilibrium community would not be changed. A further possibility is the halting of community suc- cession at some point, until the cause of this is removed from the system. Finally, the time frame of development may not be influ- enced, but the resulting tailing community may differ from the control in species com- position or abundance. Conclusion Information on benthic colonization will further improve our understanding of the long-term impacts of mine tailing discharge upon benthic communities. Such knowledge is required to determine the recovery rate of benthic communities, and in establishing whether they eventually return to their pre- discharge state, or if a new and different community results. Further, benthic colon- ization studies may be useful in ascertaining if, and how, to diminish impacts by providing necessary background information for the de- velopment of reclamation and mitigation pro- cedures. Thus, through implementation of sound resource management practices, it may be possible to substantially improve benthic habitat. Environmental regulatory agencies and industry may also refer to benthic colon- ization research when designing monitoring procedures, and establishing regulations for future marine tailing disposal systems. 68 Proceedings of the 8th Annual British Columbia Mine Reclamation Symposium in Victoria, BC, 1984. The Technical and Research Committee on Reclamation  AcknowIedgements Thanks are extended to Island Copper- Utah Mines for funding of this project. Par- ticularly, I am indebted to Island Copper's environmental department for their continual encouragement and support of the research. References Cairns, J. Jr. (ed.) 1982. Artificial Sub- strates. Ann Arbor Science Pub. Inc., Ann Arbor. 279 p. Grassle, J.F. 1980. "In-situ studies of deep- sea communities." In Advanced Con- cepts in Ocean Measurements for Ma- rine Biology. (Diemer, P.P., Vernberg, F.J. and Mirkes, D.Z., Eds.), University of South Carolina Press, South Carolina, p. 321-322. Island Copper Mine, Utah Mines Ltd. 1972-1982. Annual Environmental Assessment Reports. Leppakoski, E. 1969. "Transitory return of benthic fauna of the Bornholm Basin after extermination by oxygen insuf- ficiency." Cahiers de Biologie Marine 10: 163-172." MacArthur, R.H. and Wilson, E.G. 1967. The Theory of Island Biogeography. Prince- ton University Press, Princeton. 203 p. McCall, P.L. 1978. "Spatial-temporal distri- butions of Long Island Sound in fauna: The role of bottom disturbance in a near-shore marine habi tat ."  In Estuarine Interactions (Wiley, M.L., Ed.) Academic Press, New York. p. 191-219. Odum, E.P. 1969. "The strategy of ecosystem development." Science 164: 262-270. Pedersen, T.F. 1984. "Interstitial water met- abolite chemistry in a marine mine tail- ings deposit, Rupert Inlet, B.C." Can. J. Earth Sci. 21; 1-9. Sarnthein, M. and Richter, W. 1974. "Sub- marine experiments on benthic colon- ization of sediments in the Western Baltic Sea. I: Technical layout." Mar. Biol. 28: 159-164. Schoener, A. 1974. "Experimental zoogeog- raphy: Colonization of marine mini- islands." Am.Nat. 108: 715-738. Simberloff, D.S. and Wilson, E.O. 1969. "Ex- perimental zoogeography of the islands: The colonization of empty islands." Ecol. 50: 278-296. Simon, J.L. and Dauer, D.M. 1977. "Re- establishment of a benthic community following natural defaunation." In Ecol- ogy of Marine Benthos (Coull, B.C., Ed.), University of South Carolina Press, South Carolina, p. 139-154. 69 

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