Plankton Bloom

[Brian of Aquanauts]

About 3 weeks ago there was a large phytoplankton bloom in Weymouth/Exmouth area, people even reported it was like swimming in pea soup. We had about 10m viz at the time and were strangey quiet, but it seems to have made it's way down here to Plymouth.

It the thickest any of the skippers have ever seen, and viz is down to about 1-2m in places and 4-5m on well chosen wrecks.

Firstly the bloom is early this year, we don't normally get it till end may/first 2 weeks in June, and it's about double it's normal thickness. We have had a milder winter than normal and so the water temp hasn't dropped as much as it has previously, and so maybe this is the reason.

However I can't help thinking that there may also be other environmental factors at work, especially as the bloom seemed centred on one area initially.

Does anyone know what time of year farmers begin using nitrate fertilisers? Maybe it's due to agricultural run off. see Large Phytoplankton Blooms Fuelled by Agricultural Runoff Into Especially Vulner

It could also just be due to warmer seas, but i'm a suspicious sod.

It normally clears in 2-3 weeks but any ideas?

[Brian of Aquanauts]

Found a press release:
11 September 2006
Company leads UK in tackling water pollutant

Welcome to the Wessex Water website

snip...
Uniquely, Dorset’s geology compounds the problem locally and nitrate levels are among the highest in the UK. But, rather than build a £7m nitrate removal plant near Dorchester, Wessex Water secured the agreement of the Drinking Water Inspectorate, DWI, to trial a catchment management approach.
They now just mix the nitrate water with fresh water so that the nitrate levels are below the required regulatory standard before release. Same amount of nitrates, just diluted.

Also found out that higher levels of fertilisers are used around planting times, which are March April May.

[Brian of Aquanauts]

Just found out something else too.

Experiments are being conducted in the caves around Portland. CO2 is being injected into some of the cave systems as a way of dealing with carbon emmissions.

Also due to the large amounts of plankton around, that could be due to warmer seas, they're have been a large number of basking sharks spotted in Cornwall.

[gwilson]

We had it up in Loch Long about 4 weeks ago viz was down to about a metre, then it just dissappeared so its not just the south coast but west coast sea lochs too.

There were rumblings off submarines moving further up the Loch from Faslane causing it at the time. It might of been the remains of the CND protesters and their caravans being emptied into the water in small pieces.

[String]

I wonder if the nearly unheard of time period of constant sunshine has something to do with it.

Bloom started here about 3 weeks ago and now in full force, even offshore sites with normal 10m+ vis is down to 3m or so. A bit earlier than normal.

I dont ever remember such a dry sunny april so maybe the sunlight has something to do with it as well as temperature.

[Finless]

It's always been referred to as the 'May Bloom' in my area ......... ore, at least, diving circles.

I previous years it has usually started in April.

After my swift ascent last weekend I had a splash in Eastbourne Marina's North Harbour and the place is full of it. The wind had blown slimy mats of weed up against the wall we were jumping in off and the water was full of 'snot' as it is charmingly referred to. Obviously, harbour conditions will be warmer than the sea after the last few hot weeks ..............

It is rife locally but, AIUI, it hasn't bloomed yet. It is just sitting there waiting for the sea to warm up a bit more? Poxy stuff!!! Even after all the calm weather it was very dark at 21mtrs last weekend.

[Ian@1904]

I was looking at the water temp in Weymouth as per my Vytec - 11/12c compared to similar last year when I had 9/10c.
Does anyone have a more scientific comparison?

[resting rifleman]

Originally Posted by String

I wonder if the nearly unheard of time period of constant sunshine has something to do with it.

Bloom started here about 3 weeks ago and now in full force, even offshore sites with normal 10m+ vis is down to 3m or so. A bit earlier than normal.

I dont ever remember such a dry sunny april so maybe the sunlight has something to do with it as well as temperature.

This seems the most likely explanation to me, as a matter of fact this is the first april I can remember (weatherwise) when it has been diveable on every w/e in the month.
we have had some grim viz in the last couple of weeks but it does seem to be opening out a bit, a good blow coming up the channel and neap tides next w/e should see some improvement.
fwiw could this be 'fallout' from the ship that sank full of nitrates last year in the channel?
of course it could just be that there aint any fish left to eat the plankton
mike.

[Lou]

Plankton bloomis supposed to be daylight driven, rahter than water temp driven so the high levels of early sunlight are more likely to be responsible for the early bloom.

Although I haven't been diving, I was out kayaking off Porthleven on Saturday and we were commenting on how amazingly clear the water was comapred to a few weeks ago, so I guess it hasn't reached us yet!

[Dangerous Dan]

Las week spent a few days on the beach, and at one of the beaches Shalisbrough (sp) you couldn't see deeper than about a foot and there was scum all on the surface, but was at Whitsands bay and it looked clear,

Student life,

Dan