Limitations of DSB's - Page 7

galleon · 04-09-2003, 03:25 PM

Oh yeah, anyone else find the idea of all these DSB using hobbyists ditching their rock to pillage more every couple years disgusting?

Xwild · 04-09-2003, 04:05 PM

OK.. I've been reading this thread diligently. TRYING to make some sense of it and keep it all straight. But I've come to the conclusion that this is at least a few feet over my head. So, I need a book(s) to read that can start off with some more basic info. And some that are more advanced. So please, point me in the direction of some books.

Thanks.

MJB · 04-09-2003, 04:29 PM

I didn't miss your point at all. I just don't agree with you that there is no place for the processes that take place in the sediments in the system. And i'm not so sure I agree that THE most important vehicle for metals is detritus. Many of the most vexing metals (Se, Zn, Cd to name a few) enter the food chain because they are actively taken up from solution particularly in estuarine environments. I do agree that a high flow regime that keeps particulates suspended and more easily skimmable is preferable in the main display--Mark

SAT · 04-09-2003, 05:13 PM

Let me see if I can distill this down a bit. Spanky's argument is that detritus is captured by the sand bed where various benthic critters use it until it's no good and the residual says put. Eventually you have so much residual crap that there's no place to put it anymore and the sand bed ceases to function. Fair enough.

galleon's argument seems to be that God (or nature) didn't intend for organic matter to be processed this way. I'm not sure that God intended us to use a skimmer either, and I'm not arguing that point any further.

Let's consider two cases where we have a DSB. The first is the guy who doesn't change water, has a typical semi-working skimmer, and doesn't do anything else to export the crap. The other is the one who regularly changes water, has some decent export mechanism (high efficiency skimmer, carbon, ATS, you name it), and generally takes care of his system.

The first guy will do fine for a while because the DSB sink takes a long time to fill up. Let's say he hits the wall after 5-7 years. The system needs major surgery at this point. However, consider what might have happened if this person didn't have a DSB. I suggest he wouldn't have taken any better care of his tank. The detritus will have accumulated in a corner and the system will fail in about 2 years. Admittedly, it might be easier to fix that point, but do you think he's going to? In the end, was this person served well by the DSB or not?

There are a lot of reasons why most tanks don't last 5-7 years that have nothing to do with the filtration system.

Now consider the other case. Even if we assume that most of the processing is occuring in the sand bed, it is likely that a lot of the useless crap will escape into the water where an efficient export mechanism can pick it up. Stirring up the bed is supposedly one of the functions of the sand bed critters. At some point does the sand bed saturate to the point where it stops working? I don't know and we don't have much empirical evidence. However, Rob Toonen claimed last year to have a DSB running for over 16 years that was still going strong.

Now consider the other benefits: larger carrying capacity, no need to vacuum & greater diversity of critters (assuming you don't mind the DSB-safe limitations).

Thank you, but I'm keeping my DSB.

MJB · 04-09-2003, 05:35 PM

I think that galleon is saying (correct me if i'm wrong) that its not processed that way in the sediments around the reef and that a high flow environment will take care of any particulates by keeping them in suspension or swirled into one corner until they can be removed by whatever and accumulation of organics is not a problem. Thats probably true. But people have been trying bare bottom tanks with high flow regimes for years and still hit the wall. This discussion is not really new. Just new participants.--MJB

galleon · 04-09-2003, 05:40 PM

<<"At some point does the sand bed saturate to the point where it stops working? I don't know and we don't have much empirical evidence. ">>

We have better than empirical evidence. Look at weakly flushed, man made (or even altered natural) bays and harbors that have become eutrophic due to saturation "to the point where it stops working." Compare this to other highly flushed bays or estuaries with similar input dynamics (or, alternatively, low flush bays with less runnoff nutrient pollution) that are thriving with seagrass meadows, etc, and far from oligotrophic.

<<"I'm not sure that God intended us to use a skimmer either, and I'm not arguing that point any further.">>

Please read carefully, I posted this earlier: "We have to try to recreate conditions in nature, but we can't use nature's processes to do it. It doesn't work in closed systems."

<<"And i'm not so sure I agree that THE most important vehicle for metals is detritus. Many of the most vexing metals (Se, Zn, Cd to name a few) enter the food chain because they are actively taken up from solution particularly in estuarine environments.">>

I'm sorry you disagree with most of the world's experts on marine biogeochemistry. It is true that Se, Zn, and Cd are taken up from terrigenous input. You aren't thinking broad enough. That terrigenous input was land-based detritus, and perhaps, in the past (on a geologic scale), marine detritus. Also, much of the metals, once in solution are biogeochemically recycled from detritus to bacteria or sediment or algae, etc. etc.

galleon · 04-09-2003, 05:42 PM

<<"But people have been trying bare bottom tanks with high flow regimes for years and still hit the wall.">>

You consider D. Stuber's tanks of several decades to have hit the wall? (thats just one example, many labs have been culturing coral from closed reef systems using the bare bottom/high energy/UV/high skimming method since before D. Stuber popularized it)

SAT · 04-09-2003, 05:55 PM

Quote:

Originally posted by MJB
This discussion is not really new. Just new participants.--MJB

Aw, you take all the fun out of it!

SAT · 04-09-2003, 06:07 PM

Quote:

Originally posted by galleon
We have better than empirical evidence. Look at weakly flushed, man made (or even altered natural) bays and harbors that have become eutrophic due to saturation "to the point where it stops working." Compare this to other highly flushed bays or estuaries with similar input dynamics (or, alternatively, low flush bays with less runnoff nutrient pollution) that are thriving with seagrass meadows, etc, and far from oligotrophic.

No, that's still a theoretical argument, and it's not better than empirical evidence. You're assuming the same thing happens in an aquarium as in a harbor. That may be true, but there's no demonstration of it.

I'll concede that something like this probably can happen. Perhaps it does in many cases. To Spanky's earlier comment, not all systems are run the same. That doesn't necessarily mean all DSB's are doomed to failure. To the contrary, we have at least one case where the DSB seems to have run well for a long time.

galleon · 04-09-2003, 06:29 PM

<<"No, that's still a theoretical argument. You're assuming the same thing happens in an aquarium as in a harbor.">>

Its no assumption. You are creating an environment in the harbor/bay/whatever that becomes depositional and closed, just as in the aquarium, the major significant difference is relative volume, and even that is skewed in favor of the bay/harbor as it is. There are examples a'plenty in reef areas of the same eutrophication.

Tomascik and Sanders did a bang-up job evaluating the negative effects of this environmental alteration in a series of papers published in marine biology (Effects of eutrophication on reef-building corals).

MJB · 04-09-2003, 06:55 PM

galleon,
There are probably many examples of many systems run in many different ways that have run for ages. Look at that guy Paul B 's tank. He uses asphalt from NYC streets as LR and his system has been up since the 70's. However,if simply slapping a skimmer, and UV on the tank and cranking turnover to the hilt was the definitive answer we wouldn't be having this discussion. We've been there. At least I have. If you want to set up a tank and grow SPS with nothing but eggcrate shelving and a big ol light hanging over it thats no problem. Tons of people do it. Maybe you can't mimic nature but the processes that occur in a DSB, in seagrass beds, cryptic zones etc. bring us closer and thats what I'm srtiving for.Peace--MJB

galleon · 04-09-2003, 07:11 PM

<<"However,if simply slapping a skimmer, and UV on the tank and cranking turnover to the hilt was the definitive answer we wouldn't be having this discussion.">>

I never claimed it to be. I only used skimming as an example of a way to keep dissolved organics, that are utilized on the reef by bacterioplankton in the wild, in check.

<<"Maybe you can't mimic nature but the processes that occur in a DSB...etc. bring us closer">>

Hardly, unless a depositional environment like an algal mat or seagrass bed or eutrophic phytoplankton soup is your goal.

MJB · 04-09-2003, 07:34 PM

What else are you advocating? Sorry if I overlooked them--MJB

MJB · 04-09-2003, 08:05 PM

BBTW, I missed one of your replys. I'd like to review any data you can provide that suggests most metals entering the ocean are derived from terrigenous detritus. --MJB

galleon · 04-09-2003, 08:09 PM

<<"I'd like to review any data you can provide that suggests most metals entering the ocean are derived from terrigenous detritus.">>

I don't see where I claimed this. I did leave out the clearest cut example of terrigenous metal runoff though. As distance from land increases, iron becomes the limiting nutrient in oceanic primary productivity.