Land based sources of pollution//source estimates

Alina M. Szmant szmanta at
Wed Oct 3 12:35:49 EDT 2001

Bob and others:

Conrad Neumann and Ian MacIntyre published  the phrase years ago about 
coral reefs being "shot in the back by their own lagoons" Proc 5th Internat 
Coral Reef Congr, Tahiti 1985:  vol 3 pg 105-110), which is the Holocene 
sea level scenario you described in your email.  I agree that for some 
areas (such as Florida Keys) resuspended sediment is a major factor 
limiting coral recruitment (especially sand-blasting by coarse sediments 
during winter storms) and this may have been happening for decades if not 
longer and thus be one reason why patch reefs in Fl Keys often have higher 
coral cover and diversity than more offshore (exposed) reefs inspite of the 
lower water quality (turbidity etc) closer to shore (see Miller et all, 
Coral Reefs vol 19 (2)).  I am always amazed at the high numbers of coral 
recruits we see on these inshore patch reefs ins spite of what the text 
books tell us are unfavorable conditions.  However, bioerosion is likely 
higher inshore and not many of these patch reefs amount to much.

I have a hypothesis that I have been bandying around for a few years that 
it's been more windy since the mid 1980s and 1990s which could be an effect 
of global warming (more heat, more wind) [this is based on a gut impression 
that in spite of having bigger and better boats than I had access to in the 
1970's, we have more days that we are weathered out now than a few decades 
back].   More frequent or more severe storms all year long could result in 
lower overall water clarity in areas like the Florida Keys where there is 
lots of sediment to resuspend (I gave a presentation about all this in 
Bali, but mea culpa, mea culpa I haven't written it up yet).  If those of 
you that like to work with climate data would have access to good wind 
records, I suggest someone look at the frequency and duration of higher 
wind events over the past 50 years or more, by passing the data thru some 
kind of filter that looks for the higerh energy events (e.g. 15+ knots for 
24+ hrs):  it takes a minimum period of high winds to really get things 
stirred up, but if the rough conditions persist for too long, suspended 
sediments are likely flushed out of the system).  Thus, not enough 
resuspension could result in fine sediments building up to eventually 
become a problem (nutrients will also build up); frequent moderate energy 
events may make the system turbid a lot of the time depending on whether 
net flow rids the system of the resuspended fines; occasional major events 
help flush the system of both sediments and nutrients.  Thus wind regimes 
(and their change over time as climate changes) could make a big difference 
in the environment conditions reefs have to deal with, and their "health".

Again, things are much more complicated than one-factor causality, and the 
various factors work at different time and spatial scales.  Effects of 
elevated temperatures and over-fishing strike pretty much everywhere which 
is why I think they are at the top of my list of what needs to be addressed 
by managers; sediments and nutrients are very important in some areas and 
not others, and should be addressed where appropriate.  Some poor reef 
areas have all of the above impacting them and that is real sad.  I agree 
with those that write that we shouldn't try to make our favorite cause of 
decline be accepted by everyone as THE ONE to be concerned about, but I 
think we do need a scientifically founded way to attribute relative effects 
because whether we like it or not, that is what the managers need.

Alina Szmant

At 06:57 AM 10/03/2001 -0500, Bob Buddemeier wrote:
>List --
>Comment first, then some more discussion of (mostly sediment-related) issues.
>Special thanks to Katharina and Alina for their observations and comments.
>Katharina is right on with her comments on single variable arguments -- 
>the problem
>is, we have to understand the variables one by one to get to the point of 
>integration, and that seems to tempt a lot of people into the 
>all-or-nothing false
>dichotomy.  Another problem is the gravitation toward polar positions: 
>"reefs are
>doomed real soon because people are killing them off" vs "not too worry, 
>robust and it's just a natural fluctuation."  The first is a very slightly 
>credible position than the second, I think, but only slightly, and the 
>most useful
>synthesis combines and is offset from that discussional axis.
>Turbidity and sediment are good examples.  Without claiming that they are 
>generalizable, let's take the recent contributions to the discussion to 
>show that
>resuspension of sediment (as opposed to new input) is a significant stress 
>I suggest that this is at least partly a 'natural cycle' 
>development.  Continental
>shelves and shallow coastal areas are excellent sediment traps, retaining 
>a lot of
>what comes off the land.  Our present situation is geologically and 
>anomalous -- a relatively stable 3-6,000 year sea level high stand (the 
>range of
>times is because it's local, not eustatic, level that counts 
>operationally, and the
>Caribbean and much of the Indo-Pacific have different local sea level 
>That accounts for a lot of sediment build-up (with or without human 
>and I suggest that a number of areas may 'simply' have reached a critical 
>in terms of the inventory or load of resuspendable sediment.  A glance at the
>Pleistocene sea level curve will show why corals and reefs are not necessarily
>adapted to this kind of environment.
>I put 'simply' in quotes above to underline Katharina's point that it never is
>simple -- in this case, one of the complicating human factors is change in the
>ocean climate.  As I understand it, a number of regions of the oceans have 
>significant increases in mean wave height over the past few decades.  This 
>is the
>resuspension driver, so it may be that either natural climate cycling or
>human-induced climate change have pushed the sediment resuspension effects 
>the threshold very recently.
>This underlines a point that I hope was obvious from the earlier 
>discussions --
>reef researchers need to understand some oceanography, as well as issues of
>large-scale dynamics (the latter comment is a shameless plug for an upcoming
>special issue of Coral Reefs -- sorry).
>It also puts some other perspectives on the questions of reef doom and 
>what to do
>about it. Note that I am going to talk about a particular variable or suite of
>variables, and do not intend to imply that there aren't others, that 
>people aren't
>problems, etc.
>1.  'Land sources' in the real-time sense may not be as big a sediment 
>issue as
>often supposed.  Most large and medium -sized drainage basins have had 
>their water
>flow (for sure) and sediment discharge (proabably but not always) reduced and
>regulated by damming and diversion.  Local coastal runoff and 
>basins have the potential for dramatic increases in sediment load in 
>response to
>land use and cover changes, but the acute effects of these are often 
>localized near
>shore (although there is the general contribution to shelf sediment load 
>2.  There is no realistic prospect of modifying either the coastal zone 
>inventory or the marine energy regime, so -- if this formulation is valid --
>chronic sediment stresses in most offshore areas may be something that 
>simply has
>to be lived (or died) with.  This implies a focus on understanding its 
>to multi-stress synergism in hopes of finding a different factor that can be
>managed to reduce the combined system impact.
>3.  Conservation/preservation:  I have been beating the drum for a triage 
>to reef resarch conservation, and management, and I have also from time to 
>expressed a fondness for atolls (but outer-shelf reefs can be OK too).  I 
>that this example reinforces both -- if continental reefs really have 
>"timed out"
>in terms of Holocene habitat development, the places to look for healthy or at
>least preservable systems are in very well-flushed, no-soft-sediment 
>coastal areas
>or away from terrigenous sediment sources (e.g., ocean islands, especially 
>small land mass).
>4.  Research implications:  This point goes beyond the sediment 
>resuspension issue
>to the larger question of combined (and especially land-derived) 
>threats.  The idea
>of chronic stress build-up to a threshold transition that we are now observing
>implies not only that we are not currently working on normal or 'healthy' 
>but also that what we take as our pre-transition baseline was probably 
>affected at the subclinical level.  This means that much of the coral 
>lierature on
>function and condition has to be interpreted very cautiously if one is 
>in determining 'normal' or 'optimal' function.  Jeremy Jackson has made 
>this point
>with respect to anthropogenic ecosystem alterations; I propose extending 
>it to a
>broader suite of 'natural cycle' considerations including sediment buildup on
>shelves, the implications (for accomodation space and circulation, among other
>factors) of reef 'catch-up' with sea level, etc.
>All of which may help explain why I am of the opinion that most
>'reefs-as-we-know-them' are on their way out of the picture, especially if 
>they are
>closely associated with a major landmass.  I would rather not use 'doomed' 
>as a
>blanket statement, because I think there may be some (significantly altered)
>oceanic survivors.  The moral of the story:  Go to sea.
>Bob Buddemeier
>Katharina Fabricius wrote:
> > Hi Bob and others,
> >
> > at present the general assumption seems to be (at least here locally) that
> > turbidity is driven by physics, ie, resuspension forced by wave height,
> > depth, and particle sizes. However, present-day levels of erosion of soils
> > and discharge of sediments may increase in some areas the amount and
> > proportion of clay and other fine material, which creates greater turbidity
> > and remains suspended for longer than equal concentrations of larger
> > particles. Together with a group under Terry Done at AIMS, we just started
> > looking into modelling it all spatially, to create some sort of "turbidity
> > risk map" for the GBR (and we'd appreciate any thoughts/suggestions/
> > contributions about this).
> >
> > I also have data which show that both sediment quality (eg, concentrations
> > of transparent exopolymer particles) as well as short-term exposure to
> > sedimentation (hours to days) are important factors influencing the scope
> > of coral reefs to be recolonised by corals, and these two factors are often
> > not part of the lines of argumentation put forward by some sedimentolgists.
> >
> > With regards to the debate of whether global climate change, increasing
> > CO2, or run-off are the "greatest" threat to coral reefs, I am getting
> > worried that we may not be getting anywhere with single-cause explanations:
> > the coral reef ecosystem is so complex that reefs are dying of a thousand
> > cuts rather than of just one single cause, as each individual species and
> > life stage has its own little sensitivities to one or the other of the
> > human alterations of their environment - and what will suffer first is
> > biodiversity. But I'm also convinced that run-off is hampering the capacity
> > of reefs to recover from all sorts of disturbances: adult corals can handle
> > relatively high loads of nutrients and sediments, but recruits don't. Once
> > the adults are wiped out by COTS or bleaching, we'll wake up if the
> > juveniles are missing. That's what I'm observing here in some near-shore
> > areas of the GBR close to intense land use at present (but again, we need
> > to be cautios coming to any single-cause conclusions about our low juvenile
> > numbers: we don't have historic data on previous juvenile densities nor on
> > larvae supplies vs surviviorships from the region).
> >
> > Regards,
> > Katharina
> > (for people how may want to send me questions/comments: please apologise
> > delays in my replies, I'm off to Palau tomorrow for 3 weeks)
> >
> > At 09:59 AM 2/10/01 -0500, you wrote:
> > >Katharina, or anyone --
> > >
> > >Do you have either estimates or expert-judgement opinions on the relative
> > >extent
> > >to which (or the geographic areas in which) the observed 
> high-turbidity areas
> > >are primarily related to:
> > >a. medium or large river discharge;
> > >b. stream, small river or open coast runoff; or
> > >c. local resuspension of existing sediments?
> > >
> > >Getting some idea of the relative importance of these components of the
> > >turbidity forcing is critical to deriving impact predictions from climate,
> > >wave,
> > >and land-use models.
> > >
> > >Thanks,
> > >
> > >Bob Buddemeier
> > >
> > >Katharina Fabricius wrote:
> > >
> > > > Another, recently published study from the Indo-Pacific province, 
> in which
> > > > we looked at the effects of increasing turbidity on biodiversity:
> > > >
> > > > Fabricius KE & De'ath G (2001) Biodiversity on the Great Barrier Reef:
> > > > Large-scale patterns and turbidity-related local loss of soft coral 
> taxa.
> > > > Pp 127 - 144 in: Wolanski E (ed) Oceanographic processes of coral 
> reefs:
> > > > physical and biological links in the Great Barrier Reef. CRC Press, 
> London.
> > > >
> > > > The article is best to be read in the original book which contains a CD
> > > > with the colour images and animations of processes. In our chapter, we
> > > > present a spatial model of increasing turbidtiy (originating from a
> > > > single-point-discharge), related to decreasing biodiversity. 
> However I'm
> > > > happy to send out free reprints in paper form (black & white print) or
> > > > electronically (colour).
> > > >
> > > > Abstract:
> > > > Spatial patterns and abiotic controls of soft coral biodiversity were
> > > > determined from an extensive reef surveys on the Great Barrier Reef 
> (GBR).
> > > > Taxonomic inventories of soft corals, and estimates of cover of the 
> major
> > > > benthos forms and of the physical environment, were obtained from 161
> > > > reefs, spread relatively evenly along and across the whole GBR. 
> Reefs on
> > > > the mid-shelf between latitude 13° and 16° represented the "hotspot" of
> > > > taxonomic richness in soft corals on the GBR. Overlapping 
> distributions of
> > > > in-shore and off-shore taxa maximised richness on mid-shelf reefs.
> > > > Taxonomic richness decreased with increasing latitude, and was low and
> > > > relatively even across the shelf south of 21° lat. Soft coral 
> richness was
> > > > strongly depressed in areas of high turbidity. It was also weakly
> > > > positively related to the amount of sediment deposited, and strongly
> > > > increased with depth. Total cover of hard corals and soft corals 
> was poorly
> > > > explained by physical and spatial variables, however both varied with
> > > depth.
> > > > The findings presented here have three major management 
> implications: (1)
> > > > Turbidity and sedimentation affect the generic richness of soft corals.
> > > > Reefs with highest soft coral richness are < 20 km from the coast, well
> > > > within the range of terrestrial run-off, and hence a loss of 
> biodiversity
> > > > could result if turbidity increases due to land use practices which
> > > > generate soil loss; (2) Taxonomic composition is more strongly 
> related to
> > > > environmental conditions than total hard and soft coral cover. 
> Taxonomic
> > > > inventories are thus better indicators of environmental conditions and
> > > > human impacts than are assessments of total cover. (3) Richness and 
> cover
> > > > change more within a single site between 0 and 18 m depth, than between
> > > > reefs hundreds of kilometers apart along the shelf at the same depth.
> > > > Valuable additional information can be gained in a cost-efficient 
> way if
> > > > monitoring and survey programs covered several depth zones rather 
> than a
> > > > single depth.
> > > >
> > > > Regards,
> > > >
> > > > Katharina Fabricius
> > > >
> >
> > 
> <//\\><+><\\//><+><//\\><+><\\//><+><//\\><+><\\//><+><//\\><+><\\//><+><//\\>
> > Dr. Katharina Fabricius
> > Research Scientist
> > Australian Institute of Marine Science
> > PMB 3, Townsville Qld 4810, Australia
> > Fax +61 - 7 - 4772 5852
> > Phone +61 - 7 - 4753 4412 or 4758 1979
> > email k.fabricius at
> >
> >
> >
> > ~~~~~~~
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