I started typing you a detailed response but quit when it reached 12 paragraphs! So here is my “reduced” version. In short, I’m not a maple expert but that looks like nutrient deficiencies. I suppose some of the tip and edge browning could be attributed to lack of sufficient transpiration due to damaged roots and/or too hot and dry conditions. But I think we reduce that concern since you are growing under shade, in an organic mix kept moist. There can also be a bacterial scorch. Here is a link to summarize various scorch causes. Normally, I’d suggest taking some leaves to the County Extension Agency for a visual diagnosis and also attending local clubs to see how others grow maples in your area. But in these “unprecedented times”, that may not be an option. I also wonder what impact the length of our growing season has on deciduous leaves. Our deciduous can leaf out sooner than other parts of the country and thus might reach the end of the leaf’s period of efficient operation before environmental cues have told them to go dormant.
But in my opinion, your water quality report points to potential problems. You already know you have hard water. Which is a general way of saying you have dissolved minerals in your water that precipitate out when the water evaporates. The hardness on your report is a measure of the calcium and magnesium, which are almost always bound to carbonates and bicarbonates when present. The measure of your carbonates and bicarbonates can be found in the akalinity. Alkalinity is the water’s buffering capacity or the ability to resist change from an acid. The higher the alkalinity the more acid would be required to change the pH. So high pH (>7.0) is generally the symptom of high alkalinity water not the cause.
There are uncommon examples of water supplies with low alkalinity but a high pH, usually from the addition sodium hydroxide to raise the pH so it doesn’t leach lead from our pipes (think Flint, Michigan with their acidic river water). The bicarbonate ions measured by alkalinity form salts with calcium, magnesium, potassium, and sodium making these nutrients unavailable to the plant. When you have high calcium and carbonates in your water it will react to form calcium carbonate. This is the buildup on bonsai pots or showerheads that is the visual evidence for people to say they have hard water. Since there is an optimal range of pH for nutrient availability and uptake in plants, the prolonged impact of high alkalinity water is to shift the pH of the mix more basic (or alkaline). For some confusing reason, more basic water (>7 pH) is termed more alkaline, but that doesn’t mean it has always has higher alkalinity. Remember the example of a low alkalinity water supply treated to raise the pH (make alkaline) for health reasons.
Even though there is an optimal pH range for nutrient availability, we should also know that plants have the ability to change the pH at the root tip. Although, I suspect that this is a very localized and microscopic reaction. Some plants clearly are better at dealing with nutrient uptake outside of the optimal range. But at some point, continued irrigation with higher alkalinity water will shift the pH of the substrate more basic and outside of the range tolerated by the plant.
Across all 4 water sources from your report, the range of alkalinity is 82 – 145 ppm. The optimal level from Bailey et al 1999 is below 100 ppm for how your alkalinity is reported (as total carbonates). Hulme 2012 puts your water in a moderate alkalinity class (60 - 150ppm) and suggests that the appropriate chemical acidifying fertilizers can correct that this water quality in the nursery trade. Other options include acidifying your water to lower the alkalinity and pH. In our low annual rainfall climate, I tend to use the more restrictive greenhouse recommendations. The Bailey paper seems to be the standard and most often referenced for acceptable irrigation water quality.
My water is a similar to slightly higher range of alkalinity but also slightly lower (more acidic) pH. I try to mitigate the impact on my nursery can trees by incorporating organics (bark and peat), keeping them moist (so less calcium carbonate precipitates out), using acidic chemical fertlizers and adding elemental sulfur into the mix. For deciduous in shallow pots, I use 100% akadama with organic fertilizer and sulfur. But that still hasn’t solved all the chlorosis issues and I still occasionally fertilize with a chemical acidic fertilizer (crossing my fingers that it isn’t killing the good sulfur oxidizing bacteria). Since I haven’t conducted any controlled experiments or lab testing it is difficult to make any conclusions on the effectiveness of the sulfur. Nursery trade documents reference the limited effectiveness of sulfur since since they move their trees faster through container sizes and into the ground. Meaning the mix likely does not have the bacteria in the mix to break down the sulfur on any reasonable timescale. However, since bonsai might go years without repotting and if we are adding organic fertilizers, we may have the bacteria load necessary to use sulfur to maintain a desired pH and combat the buffering impacts of the high alkalinity irrigation water. But by only adding sulfur and not treating the water, we may still have to add supplemental macro- and micro-nutrients.
I suspect that the excess bicarbonates may be tying up too much of my calcium, so I experimented with adding gypsum (calcium sulfate) to azalea nursery cans. The experiment was too small, but I did manage to kill one with an intentional overdose. The control and correct application rate plants didn’t appear much different in terms of leaf color or growth. Since gypsum is only slightly-soluble, I suspect that not much calcium was released. Any release of sulfur would also be in the sulfate form which I don’t think would contribute a free hydrogen ion to the soil to aid in acidification. I have not experimented yet with calcium nitrate fertilizer as a calcium source.
I am excited to hear that Jonas and the Bonsai Wire Podcast plan to devote an episode to water quality and Jonas recently had a great blog post on his experiment with acidification. His water appears to fall into one of the more uncommon low akalinity, but very high pH water types. Hopefully, we can start learning how to better tailor our “soil” amendments and organic fertilizers for those of us with marginal water to improve our bonsai.
Further reading online:
Bailey, D., Bilderback, T. & Bir, D. 1999 Water considerations for container production of plants. HIL 557 North Carolina Cooperative Extension Service Raleigh, NC
Hulme F. 2012. Managing highly alkaline irrigation water. Greenhouse Product News. 22 (6):32, 34, 36.
Spectrum Analytic, Inc. Guide to Interpreting Irrigation Water Analysis