Calling all ecologists! and anyone interested in freshwater protection
August 19, 2018 4:15 AM   Subscribe

A southern NZ lake has sediments which are heavily polluted with agricultural phosphate (this is common here). A call to the science community for solutions resulted in engineered or chemical solutions only - which come with a slew of new problems. I intuit there could/should/must be a biological solution based on harvesting and community involvement.

I am very aware eutrophication is a common result of aquaculture but conventional aquaculture is not considered as a food web/network. This is a bit beyond my subject area but no one else is interested and I am ... very. I have some ideas (mainly around managed food-chains).

This is a huge topic and I don't want to get lost in the weeds - at this point I'm asking if you know of anyone attempting biological solutions to polluted natural or artificial lakes, especially phosphate pollution. Solutions could range from completely informal/grassroots or initiated by say an artist/'outsider' or early stage experimental or formal corporate or state-sector/government projects). Solutions will almost certainly use artificial supports - as long as pollutant uptake is performed by living organisms.

I have searched a lot and found little apart from a few things I know well. For instance a forestry company in my neighbourhood using its firefighting ponds to culture freshwater crayfish - and prove it's water runoff is clean.
I know of floating reedbed systems but these are problematic on windy lake surfaces. I also need to create a food interface with the sediments where the problem lies.

Solutions can range from complete food webs to single web components including:
aquatic plants
posted by unearthed to Science & Nature (12 answers total) 2 users marked this as a favorite
I recently read Braiding Sweetgrass by Robin Wall Kimmerer -- in it she describes her own efforts to de-eutrophize a pond on her property by pond-weed biomass removal. She also writes about community attempts to remediate Lake Onondaga (which has way huger problems than eutrophication). There may be some useful leads in there, or at least ideas of organizations to contact.

Do you have a nearby university with biology/ecology faculty who could be interested in making this a research project?
posted by heatherlogan at 5:32 AM on August 19, 2018 [2 favorites]

Are people applying (and confirming the effectiveness of) upstream best practices like controlling fertilizer application, construction of wetlands to treat farm runoff, etc? That is always cheaper (and more effective) than dealing with it downstream. You could also consider pass-through wetlands at the lower ends of streams feeding into the lake if nutrient reductions upstream at the individual farms was not possible.

A number of the options you are listing appear to be for human consumption, for which you would need to confirm that there were not problematic bioaccumulations (eg of cyanobacteria). The examples I know of are all wetland-based (natural or constructed wetlands with horizontal or vertical flows), which work because it is shallow and you can control the flow-through to get the desired nutrient reductions from bacteria. In lakes, where phosphorus can settle into deep sediments, those techniques don't usually apply, which is why you see so many examples of dredging and/or capping of the sediments. If the issue in your lake is not so much phosphorus settling but rather circulating in the water column, then introducing and harvesting species that take up the nutrients could work.
posted by Dip Flash at 7:17 AM on August 19, 2018 [2 favorites]

In a lot of lakes, excess phosphate leads to overgrowth of algae, which would meet your bio-control issue, but unfortunately, that kind of algae is really bad for living things. Madison, Wisconsin has phosphorous and algal bloom issues and is the location of one of the top fresh water research groups so is a good place to check out for resources.

Another bio-control option would be something like mussels but local mussels are probably not adapted to high P concentration. DO NOT introduce something invasive like zebra mussels (besides which they're not super good at getting P out of the water column). But, depending on your issue (and again, DON'T DO THIS) zebra mussels can increase water clarity so if that's your objective (high P leads to algae which leads to green water), they could be effective (high P but no algae).

In general the problem is that native species are not adapted to high P loads and introducing species into ecosystems is about as bad as/worse for ecosystems as high nutrient loads. Especially in a place like NZ with pretty limited species.
posted by hydrobatidae at 9:33 AM on August 19, 2018 [1 favorite]

Controlling the inputs and removing/ remediating in place the sediments is the best method possible if eutrophication is the only problem. I used to work in that field and the research has been done and is extensive and conclusive. If inputs cannot be stopped upstream then routing the water through wetlands will help but that's where your biomass removal can and should happen not in the lake itself. Even if you turn off all inputs today, biomass removal will not remediate the lake itself on a reasonable timescale and often makes the problem worse, not better. If phosphorus is indeed the sole issue, you need to remove (or cap or stabilize) the sediments which are the source of the phosphorus. However it is also likely that there are other issues, as eutrophication alone may or may not cause ecosystem degradation. Often there needs to be some other insult to the system to flip it over, less or more inflow, flows out of season, invasive species, mechanical disturbances etc etc.

This book is somewhat out of date but not that much and it summarizes the relevant ecology, albeit with a focus on northern Europe. But the principles remain. I suggest reading it as a starting point then following up with newer research. Here is another essay you should definitely read too as it provides another excellent summary of the science.

But in this case you have hired experts and they have given a plan. I suggest you also examine why you strongly feel they are wrong and there is a more "common sense" or cheap/ easy solution and whether that is an emotional decision and not a logical or evidence based one. Don't be the ecological version of an anti-vaxxer here, is what I'm saying.
posted by fshgrl at 1:29 PM on August 19, 2018 [2 favorites]

Also any solution that involves introducing new species or changing the food web should not and will not be considered by any ethical modern ecologist. That is how we got all these problems in the first place!!
posted by fshgrl at 1:36 PM on August 19, 2018 [1 favorite]

heatherlogan - thank you for the book I will chase it down. 'my' lake is 2.76 kmĀ² and becoming rapidly surrounded by housing and intensifying farms. It's also an intensely political issue as the various councils are trying to appease everyone.

Dip Flash - upstream thinking is not being applied (yet) in a way I find useful. My background is in catchment thinking, species, SUDS/hydrology and community engagement.

NZ has a legislated approach called Overseer (a blackbox modeling methodology/software funded by the fertiliser companies!) which is part of the problem - there is a larger problem here - successive NZ governments favouring industrial monopolies.

hydrobatidae - yes algal blooms are the primary symptom. We have other lakes here that are so toxic dogs have died from swimming in them. All and any plants and fauna would be native and only be species that already occur in the lake. Yes we have limited species but a few we do have have extensive ecological research including harvest - the freshwater crayfish and also Anguilla eels.

fshgrl - the book looks useful thanks, the essay too. Refer to reply to hydrobatidae re flora and fauna.

I didn't hire the experts - I'm a one-man-band landscape architect/ecologist annoyed by a system where siloed thinking and conventional engineering are considered solutions - I was very surprised that no biological solution had been tabled. The problem is catchment-scale and catchment thinking (networks; eco-bio; socio-cultural including Maori) is the most sustainable way to solve such problems.

Solutions so far are: sediment-capping; flocculation and lake destratification via pumping; and inceasing inflow via shutting down some irrigation (that would be good but is politically unpalatable). The first two would likely need to run for 50 years or more, hence my interest in a social-based science solution - anything more than 5 years often becomes a target of the next administratiuon and fails.

Some models I'm finding useful are:
Pollution control and in situ bioremediation for lake aquaculture using an ecological dam

fish bioturbation as a viable aquaculture technology

This paper's - Recolonisation by macrobenthos... - citations look interesting:

I'm hoping my intervention to the situation will reinvigorate public discussion and introduce the possibility of viable solutions that integrate the community, Maori (NZ's native people) along with solutions based around natural processes and hopefully some level of harvest.
posted by unearthed at 3:35 PM on August 19, 2018

All of those papers basically just repeat the fact that if you have too many nutrients they end up in the sediment and then if you disturb the sediments they become re-suspended. That is well understood and why removing the sediments is the easiest way to prevent the toxic algae blooms. Often they are pumped onto fields as fertilizer.

You cannot effectively make an adapted nutrient poor ecosystem massively more productive for a while past a certain point, which is what I think you want to do. It'll switch to a different ecosystem. There is a reason people farm carp and tilipia. And you cannot "farm" one species in the ecosystem without all kinds of knock on effects. And it would cost a lot too to do what you're saying. Plus do you really want to harvest from a lake with toxic algae blooms? That stuff is nasty.

One thing that I'd look into is diverting much of the inflow into a bio-algae system before it reaches the lake. Give free diesel to the farmers in exchange for not fertilizing near the riparian and fencing off buffers. That is the best and highest use of farm run off in my opinion. Although you still have to deal with salts etc but it's definitely the future.
posted by fshgrl at 7:07 PM on August 19, 2018 [1 favorite]

Good points fshgrl, thanks for casting your eye over the papers - there are huge levels of phosphate in the lake, there was unrestricted industrial drainage from 1910 to 1955 (>43000 Kg) and agriculture super-phosphate addition continues.

Current hard solutions are being costed at NZ$2M and I would imagine these will double, so funding is available. Yes I realise there are limits to production from the lake - as for 'harvest' it is tpoo early to say - I'm just hoping to provoke a more open discussion at first.

Pre-lake diversion, thanks - there is room for a lemma or similar approach as there's a wide water meadow before the lake. The riparian side has become a legislative nightmare/quagmire - but kiwis LOVE shiny metal solutions.
posted by unearthed at 1:50 AM on August 20, 2018 [1 favorite]

Totally off the wall idea, but what about an algal farm at the inlet to the lake. If you could take the phosphorus rich runoff water and intercept it before it goes into the lake and instead grow some useful algae (oil algae) using the water and then release clean water without the extra P back into the lake. Essentially make a farmed wetland where you are farming algae instead of whatever the farmers are growing. As a bonus given a large enough area the farmers can then plow the dried algae into their fields capturing the carbon from the algae and recycling the phosphorus in a less runoff prone form. I'm sure there are a multitude of reasons that this will not work, but even if people had a solar powered pump that is filtering out the water near their houses as mandated by the byelaws of building on the lake (assuming such byelaws can be put into place) then while it would take a long time to filter out the algae, it wouldn't take that long assuming a massively parallel continuously operating system. You would start to see benefits well before complete filtration anyways.
posted by koolkat at 3:07 AM on August 20, 2018

Well a shiny metal solution could be doable!
posted by fshgrl at 8:37 PM on August 20, 2018

koolkat - not off the wall at all especially after
fshgrl's addition - which is very, very useful, especially the Sandia page.

Thanks heaps everyone, I've now got more questions, some some more potential solution pathways and had some of my ideas challenged.
posted by unearthed at 12:49 AM on August 21, 2018

Thanks again everyone for taking part, for suggestions, feedback, links and books. It's helped a lot as I've met with people and seems to have resulted in more solutions coming forward (some just snake oil - nano-bubbles seem to be the latest!) as well as some more inclusive and holistic discussion.
posted by unearthed at 3:28 PM on September 29, 2018

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